Solid state imaging device, method of manufacturing the same, and imaging apparatus

ABSTRACT

A solid state imaging device having a light sensing section that performs photoelectric conversion of incident light includes: an insulating layer formed on a light receiving surface of the light sensing section; a layer having negative electric charges formed on the insulating layer; and a hole accumulation layer formed on the light receiving surface of the light sensing section.

RELATED APPLICATION DATA

This application is a division of U.S. patent application Ser. No.12/244,889, filed Oct. 3, 2008, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims the benefit of priority to Japanese PatentApplication JP 2007-265287 filed in the Japanese Patent Office on Oct.11, 2007, the entirety of which is incorporated by reference herein tothe extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid state imaging device capable ofsuppressing generation of a dark current, a method of manufacturing thesame, and an imaging apparatus.

2. Description of the Related Art

Solid state imaging devices, such as a CCD (charge coupled device) and aCMOS image sensor, are widely used in a video camera, a digital stillcamera, and the like. Improvement in sensitivity and noise reduction areimportant issues in all kinds of solid state imaging devices.

In particular, a dark current, which is detected as a very small currentwhen an electric charge (electron) generated from a minute defect in asubstrate interface of a light receiving surface is input as a signal,or a dark current generated due to the interface state on the interfacebetween the light sensing section and an upper layer even though thereis no pure signal charge generated by photoelectric conversion ofincident light in a state where there is no incident light is a noise tobe reduced in the solid state imaging device.

As a technique of suppressing generation of a dark current caused by theinterface state, for example, an embed type photodiode structure havinga hole accumulation layer 23 formed of a P′ layer on a light sensingsection (for example, a photodiode) 12 is used as shown in (2) of FIG.42. Moreover, in this specification, the embed type photodiode structureis referred to as an HAD (hole accumulated diode) structure. As shown in(1) of FIG. 42, in a structure where the HAD structure is not provided,electrons generated due to the interface state flow to the photodiode asa dark current. On the other hand, as shown in (2) of FIG. 38, in theHAD structure, generation of electrons from the interface is suppressedby the hole accumulation layer 23 formed on the interface. In addition,even if electric charges (electrons) are generated from the interface,the electric charges (electrons) do not flow to a charge accumulationsection, which is a potential well in an N⁺ layer of the light sensingsection 12, but flow to the hole accumulation layer 23 of the P⁺ layerin which many holes exist. Accordingly, the electric charges (electrons)can be eliminated. As a result, since it can be prevented that theelectric charges generated due to the interface are detected as a darkcurrent, the dark current caused by the interface state can besuppressed.

As a method of forming the HAD structure, it is common to perform ionimplantation of impurities for forming the P⁺ layer, for example, boron(B) or boron difluoride (BF₂) through a thermally oxidized layer or aCVD oxide layer formed on a substrate, to activate injected impuritiesby annealing, and then to form a p-type region near the interface.However, heat treatment in a high temperature of 700° C. or more isessential in order to activate doped impurities. Accordingly, formationof the hole accumulation layer using ion implantation is difficult in alow-temperature process at 400° C. or less. Also in the case of desiringto avoid long-time activation at high temperature in order to suppressdiffusion of dopant, the method of forming a hole accumulation layer inwhich ion implantation and annealing are performed is not preferable.

Furthermore, when a silicon oxide or a silicon nitride formed on anupper layer of the light sensing section is formed in a low-temperatureplasma CVD method, for example, the interface state is reduced comparedwith an interface between of a light receiving surface and a layerformed at high temperature. The reduction in interface state increases adark current.

As described above, in the case of desiring to avoid ion implantationand annealing process at high temperature, not only the holeaccumulation layer cannot be formed by known ion implantation but also adark current is further reduced. In order to solve the problem, itbecomes necessary to form a hole accumulation layer in another methodthat is not based on ion implantation in the related art.

For example, there is disclosed a technique in which charged particleshaving the same polarity as an opposite conduction type are embedded inan insulating layer formed of a silicon oxide on a photoelectricconversion element having a conduction type opposite a conduction typeof a semiconductor region formed within a semiconductor region tothereby pull up an electric potential of a surface of the photoelectricconversion section and form an inversion layer on the surface and as aresult, generation of a dark current is reduced by preventing depletionof the surface (for example, refer to JP-A-1-256168). However, in theabove technique, a technique of embedding the charged particles into theinsulating layer is needed, but it is not known which kind of embeddingtechnique is used. In addition, in order to inject electric charges intothe insulating layer from the outside as normally used in a nonvolatilememory, an electrode used to inject electric charges is needed. Even ifelectric charges can be injected from the outside in a non-contact statewithout using an electrode, the electric charges trapped in theinsulating layer are not detrapped. Accordingly, an electric chargeholding property becomes a problem. For this reason, since ahigh-quality insulating layer having a high electric charge holdingproperty is requested, it has been difficult to realize the insulatinglayer.

SUMMARY OF THE INVENTION

In order to form a sufficient hole accumulation layer by performing ionimplantation into a light sensing section (photoelectric conversionsection) in high concentration, annealing in high temperature isessential since the light sensing section is damaged by the ionimplantation. In this case, however, diffusion of impurities occurs anda photoelectric conversion characteristic deteriorates. On the otherhand, when the ion implantation is performed in low concentration inorder to reduce damage caused by the ion implantation, the concentrationof the hole accumulation layer lowers. As a result, the holeaccumulation layer does not sufficiently function as a hole accumulationlayer. That is, it is difficult to realize a sufficient holeaccumulation layer and to reduce a dark current while maintaining adesired photoelectric conversion characteristic by suppressing diffusionof impurities.

In view of the above, it is desirable to realize a sufficient holeaccumulation layer and to reduce a dark current.

According to an embodiment of the present invention, a solid stateimaging device (first solid state imaging device) having a light sensingsection that performs photoelectric conversion of incident lightincludes: an interface state lowering layer formed on a light receivingsurface of the light sensing section; a layer having negative electriccharges formed on the interface state lowering layer; and a holeaccumulation layer formed on the light receiving surface of the lightsensing section.

In the first solid state imaging device described above, since the layerhaving negative electric charges is formed on the interface statelowering layer, the hole accumulation layer is sufficiently formed onthe light-receiving-surface-side interface of the light sensing sectionby the electric field generated by negative electric charges.Accordingly, generation of electric charges (electrons) from theinterface is suppressed. In addition, even if electric charges(electrons) are generated from the interface, the electric charges(electrons) do not flow to a charge accumulation portion which is apotential well in the light sensing section but flow to the holeaccumulation layer in which many holes exist. As a result, the electriccharges (electrons) can be eliminated. As a result, since it can beprevented that the electric charges generated due to the interfacebecome a dark current and are detected by the light sensing section, adark current caused by the interface state is suppressed. Furthermore,generation of electrons due to the interface state is further suppressedsince the interface state lowering layer is formed on the lightreceiving surface of the light sensing section. As a result, it issuppressed that electrons generated due to the interface state flow tothe light sensing section as a dark current.

According to another embodiment of the present invention, a solid stateimaging device (second solid state imaging device) having a lightsensing section that performs photoelectric conversion of incident lightincludes: an insulating layer that is formed on a light receivingsurface of the light sensing section and allows the incident light to betransmitted therethrough; a negative voltage applying layer formed onthe insulating layer; and a hole accumulation layer formed on the lightreceiving surface of the light sensing section.

In the second solid state imaging device described above, since thenegative voltage applying layer is formed on the insulating layer formedon the light receiving surface of the light sensing section, the holeaccumulation layer is sufficiently formed on thelight-receiving-surface-side interface of the light sensing section bythe electric field generated when a negative voltage is applied to thenegative voltage applying layer. Accordingly, generation of electriccharges (electrons) from the interface is suppressed. In addition, evenif electric charges (electrons) are generated from the interface, theelectric charges (electrons) do not flow to a charge accumulationportion which is a potential well in the light sensing section but flowto the hole accumulation layer in which many holes exist. As a result,the electric charges (electrons) can be eliminated. As a result, sinceit can be prevented that the electric charges generated due to theinterface become a dark current and are detected by the light sensingsection, a dark current caused by the interface state is suppressed.

According to still another embodiment of the present invention, a solidstate imaging device (third solid state imaging device) having a lightsensing section that performs photoelectric conversion of incident lightincludes: an insulating layer formed on a light receiving surface of thelight sensing section; and a layer that is formed on the insulatinglayer and has a work function value larger than that of alight-receiving-surface-side interface of the light sensing section thatperforms photoelectric conversion.

In the third solid state imaging device described above, since the layerhaving a work function value larger than that of thelight-receiving-surface-side interface of the light sensing section thatperforms photoelectric conversion is provided on the insulating layerformed on the light sensing section, holes can be accumulated in thelight-receiving-side interface of the light sensing section. As aresult, a dark current is reduced.

According to still another embodiment of the present invention, a method(first manufacturing method) of manufacturing a solid state imagingdevice in which a light sensing section that performs photoelectricconversion of incident light is formed in a semiconductor substrateincludes the steps of: forming an interface state lowering layer on thesemiconductor substrate formed with the light sensing section; forming alayer having negative electric charges on the interface state loweringlayer; and forming a hole accumulation layer on a light receivingsurface of the light sensing section with the layer having negativeelectric charges.

In the method (first manufacturing method) of manufacturing a solidstate imaging device, since the layer having negative electric chargesis formed on the interface state lowering layer, the hole accumulationlayer is sufficiently formed on the light-receiving-surface-sideinterface of the light sensing section by the electric field generatedby negative electric charges. Accordingly, electric charges (electrons)generated from the interface is suppressed. In addition, even ifelectric charges (electrons) are generated from the interface, theelectric charges (electrons) do not flow to a charge accumulationportion which is a potential well in the light sensing section but flowto the hole accumulation layer in which many holes exist. As a result,the electric charges (electrons) can be eliminated. Thus, since it canbe prevented that a dark current generated by the electric charges onthe interface is detected in the light sensing section, a dark currentcaused by the interface state is suppressed. Furthermore, generation ofelectrons due to the interface state is further suppressed since theinterface state lowering layer is formed on the light receiving surfaceof the light sensing section. As a result, it is suppressed thatelectrons generated due to the interface state flow to the light sensingsection as a dark current. In addition, by using the layer havingnegative electric charges, the HAD structure can be formed without ionimplantation and annealing.

According to still another embodiment of the present invention, a method(second manufacturing method) of manufacturing a solid state imagingdevice in which a light sensing section that performs photoelectricconversion of incident light is formed in a semiconductor substrateincludes the steps of: forming an insulating layer, which allows theincident light to be transmitted therethrough, on a light receivingsurface of the light sensing section; forming a negative voltageapplying layer on the insulating layer; and forming a hole accumulationlayer on the light receiving surface of the light sensing section byapplying a negative voltage to the negative voltage applying layer.

In the method (second manufacturing method) of manufacturing a solidstate imaging device, since the negative voltage applying layer isformed on the insulating layer formed on the light receiving surface ofthe light sensing section, the hole accumulation layer is sufficientlyformed on the light-receiving-surface-side interface of the lightsensing section by the electric field generated when a negative voltageis applied to the negative voltage applying layer. Accordingly, electriccharges (electrons) generated from the interface is suppressed. Inaddition, even if electric charges (electrons) are generated from theinterface, the electric charges (electrons) do not flow to a chargeaccumulation portion which is a potential well in the light sensingsection but flow to the hole accumulation layer in which many holesexist. As a result, the electric charges (electrons) can be eliminated.Thus, since it can be prevented that a dark current generated by theelectric charges on the interface is detected in the light sensingsection, a dark current caused by the interface state is suppressed. Inaddition, by using the layer having negative electric charges, the HADstructure can be formed without ion implantation and annealing.

According to still another embodiment of the present invention, a method(third manufacturing method) of manufacturing a solid state imagingdevice in which a light sensing section that performs photoelectricconversion of incident light is formed in a semiconductor substrateincludes the steps of: forming an insulating layer on a light receivingsurface of the light sensing section; and forming a layer, which has awork function value larger than that of a light-receiving-surface-sideinterface of the light sensing section that performs photoelectricconversion, on the insulating layer.

In the method (third manufacturing method) of manufacturing a solidstate imaging device, since the layer having a work function valuelarger than that of the light-receiving-surface-side interface of thelight sensing section that performs photoelectric conversion is providedon the insulating layer formed on the light sensing section, it ispossible to form the hole accumulation layer which is formed on thelight-receiving-side interface of the light sensing section. As aresult, a dark current is reduced.

According to still another embodiment of the present invention, animaging apparatus (first imaging apparatus) includes: a condensingoptical section that condenses incident light; a solid state imagingdevice that receives the incident light condensed in the condensingoptical section and performs photoelectric conversion of the receivedlight; and a signal processing section that processes signal chargesphotoelectrically converted. The solid state imaging device includes: aninterface state lowering layer formed on a light receiving surface of alight sensing section of the solid state imaging device that performsphotoelectric conversion of the incident light; a layer having negativeelectric charges formed on the interface state lowering layer; and ahole accumulation layer formed on the light receiving surface of thelight sensing section.

In the first imaging apparatus described above, since the first solidstate imaging device according to the embodiment of the presentinvention is used, a solid state imaging device in which a dark currentis reduced can be used.

According to still another embodiment of the present invention, animaging apparatus (second imaging apparatus) includes: a condensingoptical section that condenses incident light; a solid state imagingdevice that receives the incident light condensed in the condensingoptical section and performs photoelectric conversion of the receivedlight; and a signal processing section that processes signal chargesphotoelectrically converted. The solid state imaging device includes: aninsulating layer formed on a light receiving surface of a light sensingsection of the solid state imaging device that performs photoelectricconversion of the incident light; and a negative voltage applying layerformed on the insulating layer. The insulating layer allows the incidentlight to be transmitted therethrough, and a hole accumulation layer isformed on the light receiving surface of the light sensing section.

In the second imaging apparatus described above, since the second solidstate imaging device according to the embodiment of the presentinvention is used, a solid state imaging device in which a dark currentis reduced can be used.

According to still another embodiment of the present invention, animaging apparatus (third imaging apparatus) includes: a condensingoptical section that condenses incident light; a solid state imagingdevice that receives the incident light condensed in the condensingoptical section and performs photoelectric conversion of the receivedlight; and a signal processing section that processes signal chargesphotoelectrically converted. The solid state imaging device includes: aninsulating layer formed on an upper layer of a light receiving surfaceof a light sensing section of the solid state imaging device thatconverts the incident light into signal charges; and a layer that isformed on the insulating layer and has a work function value larger thanthat of a light-receiving-surface-side interface of the light sensingsection that performs photoelectric conversion.

In the third imaging apparatus described above, since the third solidstate imaging device according to the embodiment of the presentinvention is used, a solid state imaging device in which a dark currentis reduced can be used.

In the solid state imaging device according to the embodiment of thepresent invention, a noise in an imaged image can be reduced because adark current can be suppressed. As a result, there is an advantage thata high-quality image can be obtained. In particular, generation of awhite point (point of a primary color in the case of a color CCD) due toa dark current at the time of long-time exposure with a small exposureamount can be reduced.

In the method of manufacturing a solid state imaging device according tothe embodiment of the present invention, a noise in an imaged image canbe reduced because a dark current can be suppressed. As a result, thereis an advantage that a solid state imaging device capable of obtaining ahigh-quality image can be realized. In particular, it becomes possibleto realize a solid state imaging device capable of reducing generationof a white point (point of a primary color in the case of a color CCD)due to a dark current at the time of long-time exposure with a smallexposure amount.

In the imaging apparatus according to the embodiment of the presentinvention, a noise in an imaged image can be reduced because the solidstate imaging device capable of suppressing a dark current is used. As aresult, there is an advantage that a high-quality image can be recorded.In particular, generation of a white point (point of a primary color inthe case of a color CCD) due to a dark current at the time of long-timeexposure with a small exposure amount can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating the configuration of mainparts in a solid state imaging device (first solid state imaging device)according to an embodiment (first example) of the present invention;

FIG. 2 is an energy band view explaining an effect of the solid stateimaging device (first solid state imaging device) according to theembodiment of the present invention;

FIG. 3 is a cross-sectional view illustrating the configuration of mainparts in a modification of the solid state imaging device (first solidstate imaging device);

FIG. 4 is a cross-sectional view illustrating the configuration of mainparts in a modification of the solid state imaging device (first solidstate imaging device);

FIG. 5 is a cross-sectional view illustrating the configuration of mainparts for explaining negative electric charges in a case when a layerhaving negative electric charges is in the neighborhood on a peripheralcircuit section;

FIG. 6 is a cross-sectional view illustrating the configuration of mainparts in a solid state imaging device (first solid state imaging device)according to an embodiment (second example) of the present invention;

FIG. 7 is a cross-sectional view illustrating the configuration of mainparts in a solid state imaging device (first solid state imaging device)according to an embodiment (third example) of the present invention;

FIG. 8 is a cross-sectional view illustrating a manufacturing process ina method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (first example) of the presentinvention;

FIG. 9 is a cross-sectional view illustrating a manufacturing process ina method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (first example) of the presentinvention;

FIG. 10 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (first example) of the presentinvention;

FIG. 11 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (second example) of thepresent invention;

FIG. 12 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (second example) of thepresent invention;

FIG. 13 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (second example) of thepresent invention;

FIG. 14 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (third example) of the presentinvention;

FIG. 15 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (third example) of the presentinvention;

FIG. 16 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (third example) of the presentinvention;

FIG. 17 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (fourth example) of thepresent invention;

FIG. 18 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (fourth example) of thepresent invention;

FIG. 19 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (fourth example) of thepresent invention;

FIG. 20 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (fifth example) of the presentinvention;

FIG. 21 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (fifth example) of the presentinvention;

FIG. 22 is a view illustrating the relationship between a flat bandvoltage and an oxide layer conversion thickness, which shows thatnegative electric charges exist in a hafnium oxide (HfO₂) layer;

FIG. 23 is a view for comparison of the interface state density, whichillustrates that negative electric charges exist in a hafnium oxide(HfO₂) layer;

FIG. 24 is a view illustrating the relationship between a flat bandvoltage and an oxide layer conversion thickness, which explainsformation of electrons and holes based on a thermally oxidized layer;

FIG. 25 is a cross-sectional view illustrating a manufacturing processin a method (first manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (sixth example) of the presentinvention;

FIG. 26 is a view illustrating the C-V (capacitance-voltage)characteristic of the solid state imaging device using a layer havingnegative electric charges manufactured in the sixth example of the firstmanufacturing method;

FIG. 27 is a view illustrating the C-V (capacitance-voltage)characteristic of the solid state imaging device using a layer havingnegative electric charges manufactured in the sixth example of the firstmanufacturing method;

FIG. 28 is a view illustrating the C-V (capacitance-voltage)characteristic of the solid state imaging device using a layer havingnegative electric charges manufactured in the sixth example of the firstmanufacturing method;

FIG. 29 is a cross-sectional view illustrating the configuration of mainparts in a solid state imaging device (second solid state imagingdevice) according to an embodiment (first example) of the presentinvention;

FIG. 30 is a cross-sectional view illustrating the configuration of mainparts in a solid state imaging device (second solid state imagingdevice) according to an embodiment (second example) of the presentinvention;

FIG. 31 is a cross-sectional view illustrating a manufacturing processin a method (second manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (first example) of the presentinvention;

FIG. 32 is a cross-sectional view illustrating a manufacturing processin a method (second manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (first example) of the presentinvention;

FIG. 33 is a cross-sectional view illustrating a manufacturing processin a method (second manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (first example) of the presentinvention;

FIG. 34 is a cross-sectional view illustrating a manufacturing processin a method (second manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (second example) of thepresent invention;

FIG. 35 is a cross-sectional view illustrating a manufacturing processin a method (second manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (second example) of thepresent invention;

FIG. 36 is a cross-sectional view illustrating the configuration of mainparts in a solid state imaging device (third solid state imaging device)according to an embodiment (example) of the present invention;

FIG. 37 is a cross-sectional view of the configuration of main parts,which illustrates an example of a solid state imaging device that usesan auxiliary hole accumulation layer;

FIG. 38 is a flow chart illustrating a method (third manufacturingmethod) of manufacturing a solid state imaging device according to anembodiment (example) of the present invention;

FIG. 39 is a cross-sectional view illustrating a manufacturing processin a method (third manufacturing method) of manufacturing a solid stateimaging device according to an embodiment (example) of the presentinvention;

FIG. 40 is a cross-sectional view illustrating a process ofmanufacturing main parts in a method (third manufacturing method) ofmanufacturing a solid state imaging device according to an embodiment(example) of the present invention;

FIG. 41 is a block diagram illustrating an imaging apparatus accordingto an embodiment of the present invention; and

FIG. 42 is a cross-sectional view illustrating the schematicconfiguration of a light sensing section, which shows a technique ofsuppressing generation of a dark current caused by the interface state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A solid state imaging device (first solid state imaging device)according to an embodiment (first example) of the present invention willbe described with reference to a cross-sectional view of FIG. 1illustrating the configuration of main parts.

As shown in FIG. 1, a solid state imaging device 1 includes a lightsensing section 12, which performs photoelectric conversion of incidentlight L, in a semiconductor substrate (or a semiconductor layer) 11. Ona side portion of the light sensing section 12, a peripheral circuitsection 14 in which a peripheral circuit (not specifically shown) isformed with a pixel separating region interposed therebetween isprovided. The following explanation will be made using the semiconductorsubstrate 11. On a light receiving surface 12 s of the light sensingsection (including a hole accumulation layer 23 which will be describedlater) 12, an interface state lowering layer 21 is formed. The interfacestate lowering layer 21 is formed of a silicon oxide (SiO₂) layer, forexample. On the interface state reducing layer 21, a layer 22 havingnegative electric charges is formed. Thus, the hole accumulation layer23 is formed at the light receiving surface side of the light sensingsection 12. Accordingly, at least on the light sensing section 12, theinterface state reducing layer 21 is formed in a film thickness that thehole accumulation layer 23 is formed at a side of the light receivingsurface 12 s of the light sensing section 12 by the layer 22 havingnegative electric charges. For example, the film thickness is set to beequal to or larger than one atomic layer and equal to or smaller than100 nm.

In the case when the solid state imaging device 1 is a CMOS imagesensor, for example, a pixel circuit configured to include transistors,such as a transfer transistor, a reset transistor, an amplifyingtransistor, and a selection transistor, is provided as a peripheralcircuit of the peripheral circuit section 14. In addition, a drivingcircuit which performs an operation of reading a signal on a read lineof a pixel array section formed by the plurality of light sensingsections 12, a vertical scanning circuit which transmits the readsignal, a shift register or an address decoder, a horizontal scanningcircuit, and the like are included.

Moreover, in the case when the solid state imaging device 1 is a CCDimage sensor, for example, a read gate which reads a signal chargephotoelectrically converted by the light sensing section to a verticaltransfer gate and a vertical charge transfer section which transmits theread signal charge in the vertical direction are provided as theperipheral circuit of the peripheral circuit section 14. In addition, ahorizontal charge transfer section and the like are included.

The layer 22 having negative electric charges is formed of a hafniumoxide (HfO₂) layer, an aluminum oxide (Al₂O₃) layer, a zirconium oxide(ZrO₂) layer, a tantalum oxide (Ta₂O₅) layer, or a titanium oxide (TiO₂)layer, for example. Such kinds of layers have been used as a gateinsulating layer of an insulated gate field effect transistor and thelike. Accordingly, since a layer forming method is known, the layers canbe easily formed. Examples of the layer forming method include achemical vapor deposition method, a sputtering method, and an atomiclayer deposition method. Here, it is preferable to use the atomic layerdeposition method because an SiO₂ layer which lowers the interface statecan be simultaneously formed in a thickness of 1 nm during the filmformation. In addition, as materials other than those described above, alanthanum oxide (La₂O₃), a praseodymium oxide (Pr₂O₃), a cerium oxide(CeO₂), a neodymium oxide (Nd₂O₃), a promethium oxide (Pm₂O₃), asamarium oxide (Sm₂O₃), an europium oxide (Eu₂O₃), a gadolinium oxide(Gd₂O₃), a terbium oxide (Tb₂O₃), a dysprosium oxide (Dy₂O₃), a holmiumoxide (Ho₂O₃), an erbium oxide (Er₂O₃), a thulium oxide (Tm₂O₃), anytterbium oxide (Yb₂O₃), a lutetium oxide (Lu₂O₃), an yttrium oxide(Y₂O₃), and the like may be mentioned. In addition, the layer 22 havingnegative electric charges may also be formed of a hafnium nitride layer,an aluminum nitride layer, a hafnium oxynitride layer, or an aluminumoxynitride layer.

The layer 22 having negative electric charges may have silicon (Si) ornitrogen (N) added in a range in which an insulation property is notadversely affected. The concentration is appropriately determined in arange in which an insulation property of the layer is not adverselyaffected. Thus, it becomes possible to raise the thermal resistance ofthe layer or an ability to prevent implantation of ions during a processby adding the silicon (Si) or the nitrogen (N).

An insulating layer 41 is formed on the layer 22 having negativeelectric charges, and a light shielding layer 42 is formed on theinsulating layer 41 positioned above the peripheral circuit section 14.A region where light is not incident on the light sensing section 12 isgenerated by the light shielding layer 42, and a black level in an imageis determined by an output of the light sensing section 12. In addition,since it is prevented light from being incident on the peripheralcircuit section 14, a characteristic change caused by light incident onthe peripheral circuit section is suppressed. Moreover, an insulatinglayer 43 which allows the incident light to be transmitted therethroughis formed. It is preferable that a surface of the insulating layer 43 beflat. Furthermore, a color filter layer 44 and a condensing lens 45 areformed on the insulating layer 43.

In the solid state imaging device (first solid state imaging device) 1,the layer 22 having negative electric charges is formed on the interfacestate reducing layer 21. Accordingly, an electric field is applied to asurface of the light sensing section 12 through the interface statereducing layer 21 by negative electric charges in the layer 22 havingnegative electric charges, such that the hole accumulation layer 23 isformed on the surface of the light sensing section 12.

In addition, as shown in (1) of FIG. 2, the neighborhood of theinterface can be used as the hole accumulation layer 23 by the negativeelectric charges present in the layer from immediately after forming thelayer 22 having negative electric charges. Accordingly, a dark currentgenerated by the interface state on the interface between the lightsensing section 12 and the interface state reducing layer 21 issuppressed. That is, electric charges (electrons) generated from theinterface is suppressed. In addition, even if electric charges(electrons) are generated from the interface, the electric charges(electrons) do not flow to a charge accumulation portion which is apotential well in the light sensing section 12 but flow to the holeaccumulation layer 23 in which many holes exist and accordingly, theelectric charges (electrons) can be eliminated. As a result, since itcan be prevented that a dark current generated by the electric chargeson the interface is detected in the light sensing section 12, a darkcurrent caused by the interface state is suppressed.

On the other hand, in a configuration in which the hole accumulationlayer is not provided as shown in (2) of FIG. 2, a dark current isgenerated due to the interface state. As a result, a problem that thedark current flows to the light sensing section 12 occurs. In addition,in a configuration in which the hole accumulation layer 23 is formed byion implantation as shown in (3) of FIG. 2, the hole accumulation layer23 is formed. However, since heat treatment at high temperature of 700°C. or more is essential in order to activate impurities doped in the ionimplantation as described above, the impurities are diffused to extendthe hole accumulation layer of the interface. As a result, since aregion where photoelectric conversion occurs becomes narrow, it becomesdifficult to obtain a desired photoelectric conversion characteristic.

Furthermore, in the solid state imaging device 1, generation ofelectrons due to the interface state is further suppressed since theinterface state reducing layer 21 is formed on the light receivingsurface 12 s of the light sensing section 12. As a result, it issuppressed that electrons generated due to the interface state flow tothe light sensing section 12 as a dark current.

Furthermore, in the case of using a hafnium oxide layer as the layer 22having negative electric charges, it becomes possible to obtain ananti-reflection effect as well as to form an HAD structure by optimizingthe film thickness, since the refractive index of the hafnium oxidelayer is about 2. Also in the case of materials other than the hafniumoxide layer, it becomes possible to obtain the anti-reflection effectwith a material having a high refractive index by optimizing the filmthickness.

In addition, in the case where a silicon oxide and a silicon nitridethat have been used in a known solid state imaging device are formed atlow temperature, it is known that electric charges in a layer becomepositive charges. In this case, it is difficult to form the HADstructure with negative electric charges.

Next, a modification of the solid state imaging device (first solidstate imaging device) 1 will be described with reference to across-sectional view of FIG. 3 illustrating the configuration of mainparts.

As shown in FIG. 3, a solid state imaging device 2 has ananti-reflection layer 46 formed on the layer 22 having negative electriccharges, in the case when the anti-reflection effect on the lightsensing section 12 is not sufficient only with the layer 22 havingnegative electric charges in the solid state imaging device 1. Theanti-reflection layer 46 is formed of a silicon nitride layer, forexample. In addition, the insulating layer 43 formed in the solid stateimaging device 1 is not formed. Accordingly, a color filter layer 44 anda condensing lens 45 are formed on the anti-reflection layer 46. Thus,it becomes possible to maximize the anti-reflection effect byadditionally forming the silicon nitride layer. This configuration mayalso be applied to a solid state imaging device 3 to be described later.

Thus, since reflection before light is incident on the light sensingsection 12 can be reduced by forming the anti-reflection layer 46, theamount of light incident on the light sensing section 12 can beincreased. As a result, the sensitivity of the solid state imagingdevice 2 can be improved.

Next, a modification of the solid state imaging device (first solidstate imaging device) 1 will be described with reference to across-sectional view of FIG. 4 illustrating the configuration of mainparts.

As shown in FIG. 4, a solid state imaging device 3 is obtained bydirectly forming the light shielding layer 42 on the layer 22 havingnegative electric charges without forming the insulating layer 41 in thesolid state imaging device 1. In addition, the insulating layer 43 isnot formed but the anti-reflection layer 46 is formed.

Thus, since the light shielding layer 42 is directly formed on the layer22 having negative electric charges, the light shielding layer 42 can bebrought close to the surface of the semiconductor substrate 11. As aresult, since a distance between the light shielding layer 42 and thesemiconductor substrate 11 can be narrowed, light components obliquelyincident from an upper layer of a neighboring light sensing section(photodiode), that is, optical mixed color components can be reduced.

Furthermore, when the layer 22 having negative electric charges is inthe neighborhood on the peripheral circuit section 14 as shown in FIG.5, a dark current generated due to the interface state on the surface ofthe light sensing section 12 can be suppressed by the hole accumulationlayer 23 formed by the negative electric charges of the layer 22 havingnegative electric charges. However, in the peripheral circuit section14, a potential difference occurs between a side of the light sensingsection 12 and an element 14D existing on a surface side. Accordingly,unexpected carriers flow from the surface of the light sensing section12 to the surface-side element 14D, resulting in malfunction of theperipheral circuit section 14. The configurations for avoiding suchmalfunction will be described in the following second and thirdexamples.

Next, a solid state imaging device (first solid state imaging device)according to an embodiment (second example) of the present inventionwill be described with reference to a cross-sectional view of FIG. 6illustrating the configuration of main parts. In addition, in FIG. 6, alight shielding layer for shielding a part of a light sensing sectionand a peripheral circuit section, a color filter layer for spectralfiltering of light incident on the light sensing section, a condensinglens for condensing light incident on the light sensing section, and thelike are not shown.

As shown in FIG. 6, in a solid state imaging device 4, an insulatinglayer 24 is formed between the surface of the peripheral circuit section14 and the layer 22 having negative electric charges such that adistance of the layer 22 having negative electric charges from thesurface of the peripheral circuit section 14 is larger than a distanceof the layer 22 having negative electric charges from the surface of thelight sensing section 12 in the solid state imaging device 1. Theinsulating layer 24 may be obtained by forming the interface statelowering layer 21 on the peripheral circuit section 14 to be thickerthan that on the light sensing section 12, when the interface statelowering layer 21 is formed of a silicon oxide layer.

Thus, since the insulating layer 24 is formed between the surface of theperipheral circuit section 14 and the layer 22 having negative electriccharges such that the distance of the layer 22 having negative electriccharges from the surface of the peripheral circuit section 14 is largerthan the distance of the layer 22 having negative electric charges fromthe light sensing section 12, a peripheral circuit of the peripheralcircuit section 14 is not affected by the electric field of negativeelectric charges in the layer 22 having negative electric charges. As aresult, it is possible to prevent the peripheral circuit frommalfunctioning due to the negative electric charges.

Next, a solid state imaging device (first solid state imaging device)according to an embodiment (third example) of the present invention willbe described with reference to a cross-sectional view of FIG. 7illustrating the configuration of main parts. In addition, in FIG. 7, alight shielding layer for shielding apart of a light sensing section anda peripheral circuit section, a color filter layer for spectralfiltering of light incident on the light sensing section, a condensinglens for condensing light incident on the light sensing section, and thelike are not shown.

As shown in FIG. 7, a solid state imaging device 5 is obtained byforming a layer 25 for increasing a distance between the layer havingnegative electric charges and the light receiving surface between theperipheral circuit section 14 and the layer 22 having negative electriccharges in the solid state imaging device 1. It is preferable that thelayer 25 having positive electric charges in order to eliminate aninfluence of the negative electric charges, and it is preferable to usea silicon nitride for the layer 25.

Thus, since the layer 25 having positive electric charges is formedbetween the peripheral circuit section 14 and the layer 22 havingnegative electric charges, the negative electric charges of the layer 22having negative electric charges can be reduced by the positive electriccharges in the layer 25. Accordingly, the peripheral circuit section 14is not affected by the electric field of the negative electric chargesin the layer 22 having negative electric charges. As a result, it ispossible to prevent the peripheral circuit section 14 frommalfunctioning due to the negative electric charges. As described above,the configuration in which the layer 25 having positive electric chargesis formed between the peripheral circuit section 14 and the layer 22having negative electric charges may also be applied to the solid stateimaging devices 1, 2, 3, and 4, and the same effects as in the solidstate imaging device 5 can be obtained.

Each of the solid state imaging devices 4 and 5 is configured such thata light shielding layer for shielding a part of the light sensingsection 12 and the peripheral circuit section 14, a color filter layerfor spectral filtering of light incident on at least the light sensingsection 12, a condensing lens for condensing light incident on the lightsensing section 12, and the like are provided on the layer 22 havingnegative electric charges. As an example of such a configuration, anyone of the configurations of the solid state imaging devices 1, 2, and 3may also be applied.

Next, a method (first manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (first example) of thepresent invention will be described with reference to cross-sectionalviews of a manufacturing process of FIGS. 8 to 10 illustrating mainparts. In FIGS. 8 to 10, a manufacturing process of the solid stateimaging device 1 is shown as an example.

As shown in (1) of FIG. 8, the light sensing section 12 which performsphotoelectric conversion of incident light, the pixel separating region13 for separating the light sensing section 12, the peripheral circuitsection 14 in which a peripheral circuit (not specifically shown) isformed with the pixel separating region 13 interposed between theperipheral circuit section 14 and the light sensing section 12, and thelike are formed in the semiconductor substrate (or semiconductor layer)11. A known manufacturing method is used as the manufacturing method.

Then, as shown in (2) of FIG. 8, the interface state lowering layer 21is formed on the light receiving surface 12 s of the light sensingsection 12, actually, on the semiconductor substrate 11. The interfacestate lowering layer 21 is formed of a silicon oxide (SiO₂) layer, forexample. Subsequently, the layer 22 having negative electric charges isformed on the interface state lowering layer 21. Thus, the holeaccumulation layer 23 is formed at the light receiving surface side ofthe light sensing section 12. Accordingly, at least on the light sensingsection 12, the interface state lowering layer 21 needs to be formed ina film thickness that the hole accumulation layer 23 is formed at a sideof the light receiving surface 12 s of the light sensing section 12 bythe layer 22 having negative electric charges. For example, the filmthickness is set to be equal to or larger than one atomic layer andequal to or smaller than 100 nm.

The layer 22 having negative electric charges is formed of a hafniumoxide (HfO₂) layer, an aluminum oxide (Al₂O₃) layer, a zirconium oxide(ZrO₂) layer, a tantalum oxide (Ta₂O₅) layer, or a titanium oxide (TiO₂)layer, for example. Such kinds of layers have been used as a gateinsulating layer of an insulated gate field effect transistor and thelike. Accordingly, since a layer forming method is known, the layers canbe easily formed. For example, a chemical vapor deposition method, asputtering method, and an atomic layer deposition method may be used asthe layer forming method. Here, it is preferable to use the atomic layerdeposition method because an SiO₂ layer which lowers the interface statecan be simultaneously formed in a thickness of 1 nm during the filmformation.

In addition, as materials other than those described above, a lanthanumoxide (La₂O₃), a praseodymium oxide (Pr₂O₃), a cerium oxide (CeO₂), aneodymium oxide (Nd₂O₃), a promethium oxide (Pm₂O₃), a samarium oxide(Sm₂O₃), an europium oxide (Eu₂O₃), a gadolinium oxide (Gd₂O₃), aterbium oxide (Tb₂O₃), a dysprosium oxide (Dy₂O₃), a holmium oxide(Ho₂O₃), an erbium oxide (Er₂O₃), a thulium oxide (Tm₂O₃), an ytterbiumoxide (Yb₂O₃), a lutetium oxide (Lu₂O₃), an yttrium oxide (Y₂O₃), andthe like may be used. In addition, the layer 22 having negative electriccharges may also be formed of a hafnium nitride layer, an aluminumnitride layer, a hafnium oxynitride layer, or an aluminum oxynitridelayer. These layers may also be formed by using the chemical vapordeposition, the sputtering method, or the atomic layer deposition, forexample.

In addition, the layer 22 having negative electric charges may havesilicon (Si) or nitrogen (N) added in a range in which an insulationproperty is not adversely affected. The concentration is appropriatelydetermined in a range in which an insulation property of the layer isnot adversely affected. Thus, it becomes possible to raise the thermalresistance of the layer or an ability to prevent implantation of ionsduring a process by adding the silicon (Si) or the nitrogen (N).

In addition, in the case of forming the layer 22 having negativeelectric charges with a hafnium oxide (HfO₂) layer, it becomes possibleto obtain the anti-reflection effect efficiently by adjusting the filmthickness, since the refractive index of the hafnium oxide (HfO₂) layeris about 2. Naturally, also for other kinds of layers, theanti-reflection effect can be obtained by optimizing the film thicknessaccording to the refractive index.

Then, the insulating layer 41 is formed on the layer 22 having negativeelectric charges, and then the light shielding layer 42 is formed on theinsulating layer 41. The insulating layer 41 is formed of a siliconoxide layer, for example. In addition, the light shielding layer 42 isformed of a metallic layer having a light shielding property, forexample. Thus, reaction of metal of the light shielding layer 42 and thelayer 22 having negative electric charges formed of a hafnium oxidelayer, for example, can be prevented by forming the light shieldinglayer 42 on the layer 22 having negative electric charges with theinsulating layer 41 interposed therebetween. In addition, since theinsulating layer 42 serves as an etching stopper when the lightshielding layer is etched, etching damage to the layer 22 havingnegative electric charges can be prevented.

Then, as shown in (3) of FIG. 9, a resist mask (not shown) is formed ona part of the light sensing section 12 and the light shielding layer 42positioned above the peripheral circuit section 14 by resist applicationand lithography technique and then the light shielding layer 42 isprocessed by etching using the resist mask to thereby make the lightshielding layer 42 left on the part of the light sensing section 12 andthe insulating layer 41 positioned above the peripheral circuit section14. A region where light is not incident on the light sensing section 12is generated by the light shielding layer 42, and a black level in animage is determined by an output of the light sensing section 12. Inaddition, since it is prevented light from being incident on theperipheral circuit section 14, a characteristic change caused by lightincident on the peripheral circuit section is suppressed.

Then, as shown in (4) of FIG. 9, the insulating layer 43 for reducing alevel difference caused by the light shielding layer 42 is formed on theinsulating layer 41. A surface of the insulating layer 43 is preferablyflat and is formed of a coating insulating layer, for example.

Then, as shown in (5) of FIG. 10, the color filter layer 44 is formed onthe insulating layer 43 positioned above the light sensing section 12and then the condensing lens 45 is formed on the color filter layer 44by a known manufacturing technique. In this case, a light-transmissiveinsulating layer (not shown) may be formed between the color filterlayer 44 and the condensing lens 45 in order to prevent machining damageto the color filter layer 44 at the time of lens processing. Thus, thesolid state imaging device 1 is formed.

In the first example of the method (first manufacturing method) ofmanufacturing a solid state imaging device, the layer 22 having negativeelectric charges is formed on the interface state lowering layer 21.Accordingly, by the electric field generated by negative electriccharges in the layer 22 having negative electric charges, the holeaccumulation layer 23 is sufficiently formed on thelight-receiving-surface-side interface of the light sensing section 12.Accordingly, electric charges (electrons) generated from the interfaceis suppressed. In addition, even if electric charges (electrons) aregenerated from the interface, the electric charges (electrons) do notflow to a charge accumulation portion which is a potential well in thelight sensing section 12 but flow to the hole accumulation layer 23 inwhich many holes exist. As a result, the electric charges (electrons)can be eliminated. Thus, since it can be prevented that a dark currentgenerated by the electric charges on the interface is detected in thelight sensing section, a dark current caused by the interface state issuppressed. Furthermore, generation of electrons due to the interfacestate is further suppressed since the interface state lowering layer 21is formed on the light receiving surface of the light sensing section12. As a result, it is suppressed that electrons generated due to theinterface state flow to the light sensing section 12 as a dark current.In addition, by using the layer 22 having negative electric charges, theHAD structure can be formed without ion implantation and annealing.

Next, a method (first manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (second example) of thepresent invention will be described with reference to cross-sectionalviews of a manufacturing process of FIGS. 11 to 13 illustrating mainparts. In FIGS. 11 to 13, a manufacturing process of the solid stateimaging device 2 is shown as an example.

As shown in (1) of FIG. 11, the light sensing section 12 which performsphotoelectric conversion of incident light, the pixel separating region13 for separating the light sensing section 12, the peripheral circuitsection 14 in which a peripheral circuit (not specifically shown) isformed with the pixel separating region 13 interposed between theperipheral circuit section 14 and the light sensing section 12, and thelike are formed in the semiconductor substrate (or semiconductor layer)11. A known manufacturing method is used as the manufacturing method.

Then, as shown in (2) of FIG. 11, the interface state lowering layer 21is formed on the light receiving surface 12 s of the light sensingsection 12, actually, on the semiconductor substrate 11. The interfacestate lowering layer 21 is formed of a silicon oxide (SiO₂) layer, forexample. Subsequently, the layer 22 having negative electric charges isformed on the interface state lowering layer 21. Thus, the holeaccumulation layer 23 is formed at the light receiving surface side ofthe light sensing section 12. Accordingly, at least on the light sensingsection 12, the interface state lowering layer 21 needs to be formed ina film thickness that the hole accumulation layer 23 is formed at a sideof the light receiving surface 12 s of the light sensing section 12 bythe layer 22 having negative electric charges. For example, the filmthickness is set to be equal to or larger than one atomic layer andequal to or smaller than 100 nm.

The layer 22 having negative electric charges is formed of a hafniumoxide (HfO₂) layer, an aluminum oxide (Al₂O₃) layer, a zirconium oxide(ZrO₂) layer, a tantalum oxide (Ta₂O₅) layer, or a titanium oxide (TiO₂)layer, for example. Such kinds of layers have been used as a gateinsulating layer of an insulated gate field effect transistor and thelike. Accordingly, since a layer forming method is known, the layers canbe easily formed. For example, the chemical vapor deposition method, thesputtering method, and the atomic layer deposition method may be used asthe layer forming method.

In addition, as materials other than those described above, a lanthanumoxide (La₂O₃), a praseodymium oxide (Pr₂O₃), a cerium oxide (CeO₂), aneodymium oxide (Nd₂O₃), a promethium oxide (Pm₂O₃), a samarium oxide(Sm₂O₃), an europium oxide (Eu₂O₃), a gadolinium oxide (Gd₂O₃), aterbium oxide (Tb₂O₃), a dysprosium oxide (Dy₂O₃), a holmium oxide(Ho₂O₃), an erbium oxide (Er₂O₃), a thulium oxide (Tm₂O₃), an ytterbiumoxide (Yb₂O₃), a lutetium oxide (Lu₂O₃), an yttrium oxide (Y₂O₃), andthe like may be used. In addition, the layer 22 having negative electriccharges may also be formed of a hafnium nitride layer, an aluminumnitride layer, a hafnium oxynitride layer, or an aluminum oxynitridelayer. These layers may also be formed by using the chemical vapordeposition, the sputtering method, or the atomic layer deposition, forexample. Here, it is preferable to use the atomic layer depositionmethod because an SiO₂ layer which lowers the interface state can besimultaneously formed in a thickness of 1 nm during the film formation.

In addition, the layer 22 having negative electric charges may havesilicon (Si) or nitrogen (N) added in a range in which an insulationproperty is not adversely affected. The concentration is appropriatelydetermined in a range in which an insulation property of the layer isnot adversely affected. Thus, it becomes possible to raise the thermalresistance of the layer or an ability to prevent implantation of ionsduring a process by adding the silicon (Si) or the nitrogen (N).

In addition, in the case of forming the layer 22 having negativeelectric charges with a hafnium oxide (HfO₂) layer, it becomes possibleto obtain the anti-reflection effect efficiently by adjusting the filmthickness, since the refractive index of the hafnium oxide (HfO₂) layeris about 2. Naturally, also for other kinds of layers, theanti-reflection effect can be obtained by optimizing the film thicknessaccording to the refractive index.

Then, the insulating layer 41 is formed on the layer 22 having negativeelectric charges, and then the light shielding layer 42 is formed on theinsulating layer 41. The insulating layer 41 is formed of a siliconoxide layer, for example. In addition, the light shielding layer 42 isformed of a metallic layer having a light shielding property, forexample. Thus, reaction of metal of the light shielding layer 42 and thelayer 22 having negative electric charges formed of a hafnium oxidelayer, for example, can be prevented by forming the light shieldinglayer 42 on the layer 22 having negative electric charges with theinsulating layer 41 interposed therebetween. In addition, since theinsulating layer 42 serves as an etching stopper when the lightshielding layer is etched, etching damage to the layer 22 havingnegative electric charges can be prevented.

Then, as shown in (3) of FIG. 12, a resist mask (not shown) is formed ona part of the light sensing section 12 and the light shielding layer 42positioned above the peripheral circuit section 14 by resist applicationand lithography technique and then the light shielding layer 42 isprocessed by etching using the resist mask to thereby make the lightshielding layer 42 left on the part of the light sensing section 12 andthe insulating layer 41 positioned above the peripheral circuit section14. A region where light is not incident on the light sensing section 12is generated by the light shielding layer 42, and a black level in animage is determined by an output of the light sensing section 12. Inaddition, since it is prevented light from being incident on theperipheral circuit section 14, a characteristic change caused by lightincident on the peripheral circuit section is suppressed.

Then, as shown in (4) of FIG. 12, the anti-reflection layer 46 is formedon the insulating layer 41 to cover the light shielding layer 42. Theanti-reflection layer 46 is formed of a silicon nitride layer having arefractive index of about 2, for example.

Then, as shown in (5) of FIG. 13, the color filter layer 44 is formed onthe anti-reflection layer 46 positioned above the light sensing section12 and then the condensing lens 45 is formed on the color filter layer44 by a known manufacturing technique. In this case, alight-transmissive insulating layer (not shown) may be formed betweenthe color filter layer 44 and the condensing lens 45 in order to preventmachining damage to the color filter layer 44 at the time of lensprocessing. Thus, the solid state imaging device 2 is formed.

In the second example of the method (first manufacturing method) ofmanufacturing a solid state imaging device, the same effects as in thefirst example can be obtained and reflection before light is incident onthe light sensing section 12 can be reduced by forming theanti-reflection layer 46. As a result, since the amount of lightincident on the light sensing section 12 can be increased, thesensitivity of the solid state imaging device 2 can be improved.

Next, a method (first manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (third example) of thepresent invention will be described with reference to cross-sectionalviews of a manufacturing process of FIGS. 14 to 16 illustrating mainparts. In FIGS. 14 to 16, a manufacturing process of the solid stateimaging device 3 is shown as an example.

As shown in (1) of FIG. 14, the light sensing section 12 which performsphotoelectric conversion of incident light, the pixel separating region13 for separating the light sensing section 12, the peripheral circuitsection 14 in which a peripheral circuit (not specifically shown) isformed with the pixel separating region 13 interposed between theperipheral circuit section 14 and the light sensing section 12, and thelike are formed in the semiconductor substrate (or semiconductor layer)11. A known manufacturing method is used as the manufacturing method.

Then, as shown in (2) of FIG. 14, the interface state lowering layer 21is formed on the light receiving surface 12 s of the light sensingsection 12, actually, on the semiconductor substrate 11. The interfacestate lowering layer 21 is formed of a silicon oxide (SiO₂) layer, forexample. Subsequently, the layer 22 having negative electric charges isformed on the interface state lowering layer 21. Thus, the holeaccumulation layer 23 is formed at the light receiving surface side ofthe light sensing section 12. Accordingly, at least on the light sensingsection 12, the interface state lowering layer 21 needs to be formed ina film thickness that the hole accumulation layer 23 is formed at a sideof the light receiving surface 12 s of the light sensing section 12 bythe layer 22 having negative electric charges. For example, the filmthickness is set to be equal to or larger than one atomic layer andequal to or smaller than 100 nm.

The layer 22 having negative electric charges is formed of a hafniumoxide (HfO₂) layer, an aluminum oxide (Al₂O₃) layer, a zirconium oxide(ZrO₂) layer, a tantalum oxide (Ta₂O₅) layer, or a titanium oxide (TiO₂)layer, for example. Such kinds of layers have been used as a gateinsulating layer of an insulated gate field effect transistor and thelike. Accordingly, since a layer forming method is known, the layers canbe easily formed. For example, a chemical vapor deposition method, asputtering method, and an atomic layer deposition method may be used asthe layer forming method. Here, it is preferable to use the atomic layerdeposition method because an SiO₂ layer which lowers the interface statecan be simultaneously formed in a thickness of 1 nm during the filmformation.

In addition, as materials other than those described above, a lanthanumoxide (La₂O₃), a praseodymium oxide (Pr₂O₃), a cerium oxide (CeO₂), aneodymium oxide (Nd₂O₃), a promethium oxide (Pm₂O₃), a samarium oxide(Sm₂O₃), an europium oxide (Eu₂O₃), a gadolinium oxide (Gd₂O₃), aterbium oxide (Tb₂O₃), a dysprosium oxide (Dy₂O₃), a holmium oxide(Ho₂O₃), an erbium oxide (Er₂O₃), a thulium oxide (Tm₂O₃), an ytterbiumoxide (Yb₂O₃), a lutetium oxide (Lu₂O₃), an yttrium oxide (Y₂O₃), andthe like may be used. In addition, the layer 22 having negative electriccharges may also be formed of a hafnium nitride layer, an aluminumnitride layer, a hafnium oxynitride layer, or an aluminum oxynitridelayer. These layers may also be formed by using the chemical vapordeposition, the sputtering method, or the atomic layer deposition, forexample.

In addition, the layer 22 having negative electric charges may havesilicon (Si) or nitrogen (N) added in a range in which an insulationproperty is not adversely affected. The concentration is appropriatelydetermined in a range in which an insulation property of the layer isnot adversely affected. Thus, it becomes possible to raise the thermalresistance of the layer or an ability to prevent implantation of ionsduring a process by adding the silicon (Si) or the nitrogen (N).

In addition, in the case of forming the layer 22 having negativeelectric charges with a hafnium oxide (HfO₂) layer, it becomes possibleto obtain the anti-reflection effect efficiently by adjusting the filmthickness of the hafnium oxide (HfO₂) layer. Naturally, also for otherkinds of layers, the anti-reflection effect can be obtained byoptimizing the film thickness according to the refractive index.

Then, the light shielding layer 42 is formed on the layer 22 havingnegative electric charges. The light shielding layer 42 is formed of ametallic layer having a light shielding property, for example. Thus,since the light shielding layer 42 is directly formed on the layer 22having negative electric charges, the light shielding layer 42 can bebrought close to the surface of the semiconductor substrate 11. As aresult, since a distance between the light shielding layer 42 and thesemiconductor substrate 11 can be narrowed, light components obliquelyincident from an upper layer of a neighboring photodiode, that is,optical mixed color components can be reduced.

Then, as shown in (3) of FIG. 15, a resist mask (not shown) is formed ona part of the light sensing section 12 and the light shielding layer 42positioned above the peripheral circuit section 14 by resist applicationand lithography technique and then the light shielding layer 42 isprocessed by etching using the resist mask to thereby make the lightshielding layer 42 left on the part of the light sensing section 12 andthe layer 22 having negative electric charges positioned above theperipheral circuit section 14. A region where light is not incident onthe light sensing section 12 is generated by the light shielding layer42, and a black level in an image is determined by an output of thelight sensing section 12. In addition, since it is prevented light frombeing incident on the peripheral circuit section 14, a characteristicchange caused by light incident on the peripheral circuit section issuppressed.

Then, as shown in (4) of FIG. 15, the anti-reflection layer 46 is formedon the layer 22 having negative electric charges so as to cover thelight shielding layer 42. The anti-reflection layer 46 is formed of asilicon nitride layer having a refractive index of about 2, for example.

Then, as shown in (5) of FIG. 16, the color filter layer 44 is formed onthe anti-reflection layer 46 positioned above the light sensing section12 and then the condensing lens 45 is formed on the color filter layer44 by a known manufacturing technique. In this case, alight-transmissive insulating layer (not shown) may be formed betweenthe color filter layer 44 and the condensing lens 45 in order to preventmachining damage to the color filter layer 44 at the time of lensprocessing. Thus, the solid state imaging device 3 is formed.

In the third example of the method (first manufacturing method) ofmanufacturing a solid state imaging device, the same effects as in thefirst example can be obtained and the light shielding layer 42 can bebrought close to the surface of the semiconductor substrate 11 bydirectly forming the light shielding layer 42 on the layer 22 havingnegative electric charges. As a result, since a distance between thelight shielding layer 42 and the semiconductor substrate 11 can benarrowed, light components obliquely incident from an upper layer of aneighboring photodiode, that is, optical mixed color components can bereduced. In addition, the anti-reflection effect can be maximized byforming the anti-reflection layer 46 when the anti-reflection effect isnot sufficient only with the layer 22 having negative electric charges.

Next, a method (first manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (fourth example) of thepresent invention will be described with reference to cross-sectionalviews of a manufacturing process of FIGS. 17 to 19 illustrating mainparts. In FIGS. 17 to 19, a manufacturing process of the solid stateimaging device 4 is shown as an example.

As shown in (1) of FIG. 17, the light sensing section 12 which performsphotoelectric conversion of incident light, the pixel separating region13 for separating the light sensing section 12, the peripheral circuitsection 14 in which a peripheral circuit (for example, a circuit 14C) isformed with the pixel separating region 13 interposed between theperipheral circuit section 14 and the light sensing section 12, and thelike are formed in the semiconductor substrate (or semiconductor layer)11. A known manufacturing method is used as the manufacturing method.Then, an insulating layer 26 which allows the incident light to betransmitted therethrough is formed. The insulating layer 26 is formed ofa silicon oxide layer, for example.

Then, as shown in (2) of FIG. 17, a resist mask 51 is formed on theinsulating layer 26 positioned above the peripheral circuit section 14by using resist application and lithography technique.

Then, as shown in (3) of FIG. 18, the insulating layer 26 is processedby etching using the resist mask 51 (refer to (2) of FIG. 17), leavingthe insulating layer 26 on the peripheral circuit section 14. Then, theresist mask 51 is removed.

Then, as shown in (4) of FIG. 18, the interface state lowering layer 21which covers the insulating layer 26 is formed on the light receivingsurface 12 s of the light sensing section 12, actually, on thesemiconductor substrate 11. The interface state lowering layer 21 isformed of a silicon oxide (SiO₂) layer, for example.

Then, as shown in (5) of FIG. 19, the layer 22 having negative electriccharges is formed on the interface state lowering layer 21. Thus, thehole accumulation layer 23 is formed at the light receiving surface sideof the light sensing section 12. Accordingly, at least on the lightsensing section 12, the interface state lowering layer 21 needs to beformed in a film thickness that the hole accumulation layer 23 is formedat a side of the light receiving surface 12 s of the light sensingsection 12 by the layer 22 having negative electric charges. Forexample, the film thickness is set to be equal to or larger than oneatomic layer and equal to or smaller than 100 nm.

The layer 22 having negative electric charges is formed of a hafniumoxide (HfO₂) layer, an aluminum oxide (Al₂O₃) layer, a zirconium oxide(ZrO₂) layer, a tantalum oxide (Ta₂O₅) layer, or a titanium oxide (TiO₂)layer, for example. Such kinds of layers have been used as a gateinsulating layer of an insulated gate field effect transistor and thelike. Accordingly, since a layer forming method is known, the layers canbe easily formed. For example, a chemical vapor deposition method, asputtering method, and an atomic layer deposition method may be used asthe layer forming method. Here, it is preferable to use the atomic layerdeposition method because an SiO₂ layer which lowers the interface statecan be simultaneously formed in a thickness of 1 nm during the filmformation.

In addition, as materials other than those described above, a lanthanumoxide (La₂O₃), a praseodymium oxide (Pr₂O₃), a cerium oxide (CeO₂), aneodymium oxide (Nd₂O₃), a promethium oxide (Pm₂O₃), a samarium oxide(Sm₂O₃), an europium oxide (Eu₂O₃), a gadolinium oxide (Gd₂O₃), aterbium oxide (Tb₂O₃), a dysprosium oxide (Dy₂O₃), a holmium oxide(Ho₂O₃), an erbium oxide (Er₂O₃), a thulium oxide (Tm₂O₃), an ytterbiumoxide (Yb₂O₃), a lutetium oxide (Lu₂O₃), an yttrium oxide (Y₂O₃), andthe like may be used. In addition, the layer 22 having negative electriccharges may also be formed of a hafnium nitride layer, an aluminumnitride layer, a hafnium oxynitride layer, or an aluminum oxynitridelayer. These layers may also be formed by using the chemical vapordeposition, the sputtering method, or the atomic layer deposition, forexample.

In addition, the layer 22 having negative electric charges may havesilicon (Si) or nitrogen (N) added in a range in which an insulationproperty is not adversely affected. The concentration is appropriatelydetermined in a range in which an insulation property of the layer isnot adversely affected. Thus, it becomes possible to raise the thermalresistance of the layer or an ability to prevent implantation of ionsduring a process by adding the silicon (Si) or the nitrogen (N).

In addition, in the case of forming the layer 22 having negativeelectric charges with a hafnium oxide (HfO₂) layer, it becomes possibleto obtain the anti-reflection effect efficiently by adjusting the filmthickness, since the refractive index of the hafnium oxide (HfO₂) layeris about 2. Naturally, also for other kinds of layers, theanti-reflection effect can be obtained by optimizing the film thicknessaccording to the refractive index.

The solid state imaging device 4 is configured such that a lightshielding layer for shielding a part of the light sensing section 12 andthe peripheral circuit section 14, a color filter layer for spectralfiltering of light incident on at least the light sensing section 12, acondensing lens for condensing light incident on the light sensingsection 12, and the like are provided on the layer 22 having negativeelectric charges. As an example of such a configuration, any one of theconfigurations of the solid state imaging devices 1, 2, and 3 may alsobe applied.

In the fourth example of the method (first manufacturing method) ofmanufacturing a solid state imaging device, the layer 22 having negativeelectric charges is formed on the interface state lowering layer 21.Accordingly, by the electric field generated by negative electriccharges in the layer 22 having negative electric charges, the holeaccumulation layer 23 is sufficiently formed on thelight-receiving-surface-side interface of the light sensing section 12.Accordingly, electric charges (electrons) generated from the interfacecan be suppressed. In addition, even if electric charges (electrons) aregenerated from the interface, the electric charges (electrons) do notflow to a charge accumulation portion which is a potential well in thelight sensing section 12 but flow to the hole accumulation layer 23 inwhich many holes exist. As a result, the electric charges (electrons)can be eliminated. Thus, since it can be prevented that a dark currentgenerated by the electric charges on the interface is detected in thelight sensing section, a dark current caused by the interface state issuppressed. Furthermore, generation of electrons due to the interfacestate is further suppressed since the interface state lowering layer 21is formed on the light receiving surface of the light sensing section12. As a result, it is suppressed that electrons generated due to theinterface state flow to the light sensing section 12 as a dark current.In addition, by using the layer 22 having negative electric charges, theHAD structure can be formed without ion implantation and annealing.

In addition, since the insulating layer 26 is formed on the peripheralcircuit section 14, a distance to the layer 22 having negative electriccharges on the peripheral circuit section 14 becomes larger than adistance to the layer having negative electric charges on the lightsensing section 12. As a result, the negative electric field appliedfrom the layer 22 having negative electric charges to the peripheralcircuit section 14 is reduced. That is, since an influence of the layer22 having negative electric charges on the peripheral circuit section 14is reduced, malfunction of the peripheral circuit section 14 caused bythe negative electric field generated by the layer 22 having negativeelectric charges is prevented.

Next, a method (first manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (fifth example) of thepresent invention will be described with reference to cross-sectionalviews of a manufacturing process of FIGS. 20 and 21 illustrating mainparts. In FIGS. 20 and 21, a manufacturing process of the solid stateimaging device 4 is shown as an example.

As shown in (1) of FIG. 20, the light sensing section 12 which performsphotoelectric conversion of incident light, the pixel separating region13 for separating the light sensing section 12, the peripheral circuitsection 14 in which a peripheral circuit (for example, a circuit 14C) isformed with the pixel separating region 13 interposed between theperipheral circuit section 14 and the light sensing section 12, and thelike are formed in the semiconductor substrate (or semiconductor layer)11. A known manufacturing method is used as the manufacturing method.Then, the interface state lowering layer 21 which allows the incidentlight to be transmitted therethrough is formed. The interface statelowering layer 21 is formed of a silicon oxide layer, for example. Then,a layer 25 for separating the layer having negative electric chargesfrom the surface of the light receiving surface is formed on theinterface state lowering layer 21. It is preferable that the layer 25having positive electric charges in order to eliminate an influence ofthe negative electric charges, and it is preferable to use a siliconnitride for the layer 25.

At least on the light sensing section 12, the interface state loweringlayer 21 needs to be formed in a film thickness that the holeaccumulation layer 23, which will be described later, is formed at aside of the light receiving surface 12 s of the light sensing section 12by the layer 22 having negative electric charges formed later. Forexample, the film thickness is set to be equal to or larger than oneatomic layer and equal to or smaller than 100 nm.

Then, as shown in (2) of FIG. 20, a resist mask 52 is formed on thelayer 25 having positive electric charges positioned above theperipheral circuit section 14 by using resist application andlithography technique.

Then, as shown in (3) of FIG. 21, the layer 25 having positive electriccharges is processed by etching using the resist mask 52 (refer to (2)of FIG. 20), leaving the layer 25 having positive electric charges onthe peripheral circuit section 14. Then, the resist mask 52 is removed.

Then, as shown in (4) of FIG. 21, the layer 22 having negative electriccharges which covers the layer 25 having positive electric charges isformed on the interface state lowering layer 21.

The layer 22 having negative electric charges is formed of a hafniumoxide (HfO₂) layer, an aluminum oxide (Al₂O₃) layer, a zirconium oxide(ZrO₂) layer, a tantalum oxide (Ta₂O₅) layer, or a titanium oxide (TiO₂)layer, for example. Such kinds of layers have been used as a gateinsulating layer of an insulated gate field effect transistor and thelike. Accordingly, since a layer forming method is known, the layers canbe easily formed. For example, a chemical vapor deposition method, asputtering method, and an atomic layer deposition method may be used asthe layer forming method. Here, it is preferable to use the atomic layerdeposition method because an SiO₂ layer which lowers the interface statecan be simultaneously formed in a thickness of 1 nm during the filmformation.

In addition, as materials other than those described above, a lanthanumoxide (La₂O₃), a praseodymium oxide (Pr₂O₃), a cerium oxide (CeO₂), aneodymium oxide (Nd₂O₃), a promethium oxide (Pm₂O₃), a samarium oxide(Sm₂O₃), an europium oxide (Eu₂O₃), a gadolinium oxide (Gd₂O₃), aterbium oxide (Tb₂O₃), a dysprosium oxide (Dy₂O₃), a holmium oxide(Ho₂O₃), an erbium oxide (Er₂O₃), a thulium oxide (Tm₂O₃), an ytterbiumoxide (Yb₂O₃), a lutetium oxide (Lu₂O₃), an yttrium oxide (Y₂O₃), andthe like may be used. In addition, the layer 22 having negative electriccharges may also be formed of a hafnium nitride layer, an aluminumnitride layer, a hafnium oxynitride layer, or an aluminum oxynitridelayer. These layers may also be formed by using the chemical vapordeposition, the sputtering method, or the atomic layer deposition, forexample.

In addition, the layer 22 having negative electric charges may havesilicon (Si) or nitrogen (N) added in a range in which an insulationproperty is not adversely affected. The concentration is appropriatelydetermined in a range in which an insulation property of the layer isnot adversely affected. Thus, it becomes possible to raise the thermalresistance of the layer or an ability to prevent implantation of ionsduring a process by adding the silicon (Si) or the nitrogen (N).

In addition, in the case of forming the layer 22 having negativeelectric charges with a hafnium oxide (HfO₂) layer, it becomes possibleto obtain the anti-reflection effect efficiently by adjusting the filmthickness of the hafnium oxide (HfO₂) layer. Naturally, also for otherkinds of layers, the anti-reflection effect can be obtained byoptimizing the film thickness according to the refractive index.

The solid state imaging device 5 is configured such that a lightshielding layer for shielding a part of the light sensing section 12 andthe peripheral circuit section 14, a color filter layer for spectralfiltering of light incident on at least the light sensing section 12, acondensing lens for condensing light incident on the light sensingsection 12, and the like are provided on the layer 22 having negativeelectric charges. As an example of such a configuration, any one of theconfigurations of the solid state imaging devices 1, 2, and 3 may alsobe applied.

In the fifth example of the method (first manufacturing method) ofmanufacturing a solid state imaging device, the layer 22 having negativeelectric charges is formed on the interface state lowering layer 21.Accordingly, by the electric field generated by negative electriccharges in the layer 22 having negative electric charges, the holeaccumulation layer 23 is sufficiently formed on thelight-receiving-surface-side interface of the light sensing section 12.Accordingly, electric charges (electrons) generated from the interfacecan be suppressed. In addition, even if electric charges (electrons) aregenerated from the interface, the electric charges (electrons) do notflow to a charge accumulation portion which is a potential well in thelight sensing section 12 but flow to the hole accumulation layer 23 inwhich many holes exist. As a result, the electric charges (electrons)can be eliminated. Thus, since it can be prevented that a dark currentgenerated by the electric charges on the interface is detected in thelight sensing section, a dark current caused by the interface state issuppressed. Furthermore, generation of electrons due to the interfacestate is further suppressed since the interface state lowering layer 21is formed on the light receiving surface of the light sensing section12. As a result, it is suppressed that electrons generated due to theinterface state flow to the light sensing section 12 as a dark current.In addition, by using the layer 22 having negative electric charges, theHAD structure can be formed without ion implantation and annealing.

In addition, since the layer 25 which preferably has positive electriccharges and serves to separate the layer having negative electriccharges from the surface of the light receiving surface is formedbetween the peripheral circuit section 14 and the layer 22 havingnegative electric charges, the negative electric charges of the layer 22having negative electric charges is reduced by the positive electriccharges in the layer 25 having positive electric charges. Accordingly,the peripheral circuit section 14 is not affected by the electric fieldof the negative electric charges in the layer 22 having negativeelectric charges. As a result, it is possible to prevent the peripheralcircuit section 14 from malfunctioning due to the negative electriccharges.

Here, it will be described below that negative electric charges exist inthe hafnium oxide (HfO₂) layer which is an example of the layer havingnegative electric charges.

As a first sample, one which is a MOS capacitor having a gate electrodeformed on a silicon substrate with a thermally-oxidized silicon (SiO₂)layer interposed therebetween and in which the film thickness of thethermally-oxidized silicon layer is changed is prepared.

As a second sample, one which is a MOS capacitor having a gate electrodeformed on a silicon substrate with a CVD silicon oxide (CVD-SiO₂) layerinterposed therebetween and in which the film thickness of the CVDsilicon oxide layer is changed is prepared.

As a third sample, one which is a MOS capacitor having a gate electrodeformed on a silicon substrate with a laminated layer, which is obtainedby sequentially laminating an ozone-silicon oxide (O₃—SiO₂) layer, ahafnium oxide (HfO₂) layer, and a CVD silicon oxide (SiO₂) layer,interposed therebetween and in which the film thickness of the CVDsilicon oxide layer is changed is prepared. In addition, the filmthicknesses of the HfO₂ layer and O₃—SiO₂ layer are fixed.

The CVD-SiO₂ layer of each sample is formed by a CVD method of usingmixed gas of monosilane (SiH₄) and oxygen (O₂), and the HfO₂ layer isformed by an ALD method of using tetrakisethylmethyl-amino hafnium(TEMAHf) and ozone (O₃) as materials. The O₃—SiO₂ layer of the thirdsample is an interface oxide layer which has a thickness of about 1 nmand is formed between the HfO₂ layer and the silicon substrate whenforming the HfO₂ layer in the ALD method. For each gate electrode ineach of the samples, a structure in which an aluminum (Al) layer, atitanium nitride (TiN) layer, and a titanium (Ti) layer are laminatedfrom above is used.

In the above sample structures, the gate electrode is formed immediatelyon the SiO₂ layer in the case of the first and second samples, but theCVD-SiO₂ layer is laminated on the HfO₂ layer only in the case of thethird sample where the HfO₂ layer is applied. This is to prevent theHfO₂ and the electrode from reacting with each other on the interfacewhen the HfO₂ and the gate electrode are made to come in direct contactwith each other.

Furthermore, in the laminated structure of the third sample, thethickness of the HfO₂ layer is fixed to 10 nm and the film thickness ofthe upper CVD-SiO₂ layer is changed. The reason is because the HfO₂ hasa large relative permittivity and accordingly, the HfO₂ layer has athickness of several nanometers when the thickness is calculated as athickness of the oxide layer even if the HfO₂ layer is formed in a filmthickness of 10 nm. As a result, it becomes difficult to see a change ofa flat band voltage Vfb with respect to an oxide layer conversionthickness.

For the first, second, and third samples, the flat band voltage Vfbaccording to an oxide layer conversion thickness Tox has been examined.The result is shown in FIG. 22.

As shown in FIG. 22, in the cases of the first sample of thethermally-oxidized (Thermal-SiO₂) layer and second sample of theCVD-SiO₂ layer, the flat band voltage shifts in a minus directionaccording to an increase in the film thickness. On the other hand, onlyin the third sample where the HfO₂ layer is applied, it has beenconfirmed that the flat band voltage shifts in a plus directionaccording to the increase in film thickness. By the behavior of the flatband voltage, it can be seen that negative electric charges exist in theHfO₂ layer. In addition, it can be seen that each material, which formsa layer having negative electric charges, other than the HfO₂ also hasnegative electric charges, similar to the HfO₂.

In addition, data of the interface state density in each sample is shownin FIG. 23. In FIG. 23, comparison of the interface state density Dithas been performed by using the first, second, and third samples inwhich Tox in FIG. 22 is almost equal in about 40 nm.

As a result, as shown in FIG. 23, while the first sample of thethermally-oxidized (Thermal-SiO₂) layer has a characteristic of 2E10(/cm²·eV) or less, the interface state is reduced by about one order ofmagnitude in the second sample of the CVD-SiO₂ layer. On the other hand,in the case of the third sample using the HfO₂ layer, it has beenconfirmed that about 3E10/cm²·eV and a good interface close to thethermally oxidized layer. In addition, it can be seen that eachmaterial, which forms a layer having negative electric charges, otherthan the HfO₂ also has the good interface close to the thermallyoxidized layer, similar to the HfO₂.

Next, a flat band voltage Vfb with respect to the oxide layer conversionthickness Tox when the layer 25 having positive electric charges wasformed has been examined. The result is shown in FIG. 24.

As shown in FIG. 24, in a case larger than the flat band voltage of thethermally oxidized layer, a hole is formed on a surface of the silicon(Si) because a negative electric charge exists in the layer. An exampleof such a laminated layer includes one obtained by laminating an HfO₂layer and a CVD-SiO₂ layer on a surface of a silicon (Si) substratesequentially from below. On the other hand, in a case smaller than theflat band voltage of the thermally oxidized layer, an electron is formedon the silicon (Si) surface because a positive electric charge exists inthe layer. An example of such a laminated layer includes one obtained bylaminating a CVD-SiO₂ layer, a CVD-SiN layer, an HfO₂ layer, and aCVD-SiO₂ layer on a surface of a silicon (Si) substrate sequentiallyfrom below. Here, when the film thickness of the CVD-SiN layer is madelarge, a flat band voltage becomes large compared with a thermallyoxidized layer, shifting in the negative direction. Furthermore, aninfluence of the negative electric charges of the hafnium oxide (HfO₂)is eliminated by the positive electric charges in the CVD-SiN layer.

In the solid state imaging devices 1 to 5 in the above examples, in thecase of containing nitrogen (N) in the layer 22 having negative electriccharges as described above, the nitrogen (N) may be contained bynitriding treatment using high-frequency plasma or microwave plasmaafter forming the layer 22 having negative electric charges. Inaddition, the negative electric charges in the layer may be increased byexecuting electron beam curing processing using electron beamirradiation on the layer 22 having negative electric charges afterforming the layer 22 having negative electric charges.

Next, a preferable manufacturing method (sixth example) when a hafniumoxide is used for the layer 22 having negative electric charges whichhas been used in the methods of manufacturing a solid state imagingdevice in the first to fifth examples of the present invention will bedescribed below with reference to FIG. 25. As an example, FIG. 25 showsa case suitable for the first example of the first manufacturing method.A method of forming the layer having negative electric charges in theembodiment of the present invention may also be applied to methods offorming the layer having negative electric charges in the second tofifth examples of the first manufacturing method in the same manner.

When the layer 22 having negative electric charges is formed of ahafnium oxide using an atomic layer deposition method (ALD method), thefilm quality is excellent. However, there is a problem that it takes atime for film formation. Therefore, as shown in (1) of FIG. 25, there isprepared the semiconductor substrate (or semiconductor layer) 11 inwhich the light sensing section 12 which performs photoelectricconversion of incident light, the pixel separating region 13 forseparating the light sensing section 12, the peripheral circuit section14 having a peripheral circuit (not specifically shown) formed with thepixel separating region 13 interposed between the peripheral circuitsection 14 and the light sensing section 12, and the like are formed,and the interface state lowering layer 21 is formed on the lightreceiving surface 12 s of the light sensing section 12, actually, on thesemiconductor substrate 11. Then, a first hafnium oxide layer 22-1 isformed on the interface state lowering layer 21 using the atomic layerdeposition method. The first hafnium oxide layer 22-1 is formed in afilm thickness of at least 3 nm of the film thickness required for thelayer 22 having negative electric charges.

In an example of a film forming condition of the atomic layer depositionmethod (ALD method) for forming the first hafnium oxide layer 22-1,TEMA-Hf (tetrakis ethylmethylamido hafnium), TDMA-Hf (tetrakisdimethylamido hafnium) or TDEA-Hf (tetrakis diethylamido hafnium) isused as a precursor, the temperature of the substrate at the time offilm formation is set to 200° C. to 500° C., the flow rate of precursoris set to 10 cm³/min to 500 cm³/min, the irradiation time of precursoris 1 second to 15 seconds, and the flow rate of ozone (O₃) is set to 5cm³/min to 50 cm³/min.

Alternatively, the first hafnium oxide layer 22-1 may also be formed byusing a metal organic chemical vapor deposition (MOCVD method). In anexample of a film forming condition in the case, TEMA-Hf (tetrakisethylmethylamido hafnium), TDMA-Hf (tetrakis dimethylamido hafnium) orTDEA-Hf (tetrakis diethylamido hafnium) is used as a precursor, thetemperature of the substrate at the time of film formation is set to200° C. to 600° C., the flow rate of precursor is set to 10 cm³/min to500 cm³/min, the irradiation time of precursor is 1 second to 15seconds, and the flow rate of ozone (O₃) is set to 5 cm³/min to 50cm³/min.

Then, as shown in (2) of FIG. 25, a second hafnium oxide layer 22-2 isformed on the first hafnium oxide layer 22-1 by using a physical vapordeposition method (PVD method), completing the layer 22 having negativeelectric charges. For example, the film formation is performed such thatthe film thickness including the first hafnium oxide layer 22-1 and thesecond hafnium oxide layer 22-2 is set to 50 nm to 60 nm. Then, asdescribed in the first to fifth examples, subsequent processing forforming the insulating layer 41 on the layer 22 having negative electriccharges is performed.

In an example of a film forming condition in the physical vapordeposition method (PVD method) for forming the second hafnium oxidelayer 22-2, a hafnium metal target is used as a target, argon and oxygenare used as process gas, the pressure of film forming atmosphere is setto 0.01 Pa to 50 Pa, power is set to 500 W to 2.00 kW, the flow rate ofargon (Ar) is set to 5 cm³/min to 50 cm³/min, and the flow rate ofoxygen (O₂) is set to 5 cm³/min to 50 cm³/min.

Next, the C-V (capacitance-voltage) characteristic of the solid stateimaging device has been examined in a condition that the thickness ofthe layer 22 having negative electric charges, which is formed of ahafnium oxide, is set to 60 nm and the thickness of the first hafniumoxide layer 22-1 is used as a parameter. The result is shown in FIGS. 26and 27. In FIGS. 26 and 27, a vertical axis indicates a capacitance (C)and a horizontal axis indicates a voltage (V).

As shown in FIG. 26, in the case when a hafnium oxide (HfO₂) layer isformed only by the PVD method, the flat band voltage Vfb is −1.32 Vwhich is a negative voltage. This is not sufficient for a layer havingnegative electric charges. In order to be a layer having negativeelectric charges, the flat band voltage Vfb needs to be a positivevoltage. In addition, since a rising edge is blunt, the interface statedensity is increased. In this case, it was evaluated that the interfacestate density Dit was too high to be applied, which will be describedlater.

On the other hand, in the case when the first hafnium oxide layer 22-1is formed in a thickness of 3 nm by using the ALD method and then thesecond hafnium oxide layer 22-2 is formed on the first hafnium oxidelayer 22-1 in a thickness of 50 nm by using the PVD method, the flatband voltage Vfb is +0.42 V which is a positive voltage. Accordingly,the layer having negative electric charges is obtained. In addition,since a rising edge is sharp, the interface state density Dit is low,resulting in Dit=5.14E10/cm²·eV.

In addition, in the case when the first hafnium oxide layer 22-1 isformed in a thickness of 11 nm by using the ALD method and then thesecond hafnium oxide layer 22-2 is formed on the first hafnium oxidelayer 22-1 in a thickness of 50 nm by using the PVD method, the flatband voltage Vfb becomes a positive voltage which is further increased.Accordingly, the layer having negative electric charges is obtained. Inaddition, since a rising edge is sharper, the interface state densityDit is low.

Furthermore, as shown in FIG. 27, in the case when the first hafniumoxide layer 22-1 is formed in a thickness of 11 nm by using the ALDmethod and then the second hafnium oxide layer 22-2 is formed on thefirst hafnium oxide layer 22-1 in a thickness of 50 nm by using the PVDmethod, the flat band voltage Vfb close to that in a case when theentire layer 22 having negative electric charges is formed by using theALD method and the rising edge also has an almost similar state.

Next, for the layer having negative electric charges obtained by formingthe first hafnium oxide layer 22-1 in a thickness of 11 nm and thenforming the second hafnium oxide layer 22-2 on the first hafnium oxidelayer 22-1 in a thickness of 50 nm using the PVD method, typicalmeasurement (Qs-CV: Quasi-static-CV) of the C-V characteristic using adirect current and measurement (Hf-CV) using a high frequency wereperformed. The Qs-CV measurement is a measurement method of sweeping agate voltage as a linear function of time and calculating a displacementcurrent flowing between a gate and a substrate. From this, a capacitancein a low-frequency region is obtained. The result is shown in FIG. 28.In addition, the interface state density Dit is calculated from adifference between a measurement value of Qs-CV and a measurement valueof Hf-CV. As a result, since the interface state density Dit becomes5.14E10/cm²·eV, a sufficiently low value is obtained. In addition, asdescribed above, since the flat band voltage Vfb is +0.42V, a positivevoltage is obtained.

Thus, by forming the first hafnium oxide layer 22-1 in a thickness of 3nm or more, a value of the flat band voltage Vfb of the layer 22 havingnegative electric charges can be set to have a positive voltage and theinterface state density Dit can be made low. Accordingly, the firsthafnium oxide layer 22-1 is preferably formed in a film thickness of atleast 3 nm of the film thickness required for the layer 22 havingnegative electric charges.

The first hafnium oxide layer 22-1 is a layer formed by the atomic layerdeposition method. If the film thickness is smaller than 3 nm in formingthe hafnium oxide layer using the atomic layer deposition method,interface damage resulting from the PVD method occurs when the followingsecond hafnium oxide layer 22-2 is formed by using the PVD method.However, if the thickness of the first hafnium oxide layer 22-1 is 3 nmor more, the interface damage is suppressed even if the following secondhafnium oxide layer 22-2 is formed by using the PVD method. Thus, bysetting the thickness of the first hafnium oxide layer 22-1 to 3 nm ormore so that the interface damage resulting from the PVD method issuppressed, a value of the flat band voltage Vfb of a layer includingthe first hafnium oxide layer 22-1 and the second hafnium oxide layer22-2 becomes a positive voltage. As a result, the layer including thefirst hafnium oxide layer 22-1 and the second hafnium oxide layer 22-2becomes a layer having negative electric charges. For this reason, thefirst hafnium oxide layer 22-1 formed at a side of the interface withthe interface state lowering layer 21 is made to have a film thicknessof 3 nm or more. In addition, an example of the PVD method includes asputtering method.

On the other hand, if the entire layer 22 having negative electriccharges is formed by using the atomic layer deposition method, anexcellent C-V characteristic is obtained, but the productivitysignificantly lowers because it takes too much time to form the layer.For this reason, the thickness of the first hafnium oxide layer 22-1cannot be made too large. In the atomic layer deposition method, ittakes about 45 minutes to form a hafnium oxide layer in a thickness of10 nm, for example. On the other hand, in the case of a physical vapordeposition method, it takes about 3 minutes to form a hafnium oxidelayer in a thickness of 50 nm, for example. Accordingly, an upper limitof the thickness of the first hafnium oxide layer 22-1 is determinedtaking the productivity into consideration. For example, when the layerforming time of the layer 22 having negative electric charges is set to1 hour or less, the upper limit of the thickness of the first hafniumoxide layer 22-1 is about 11 nm to 12 nm. Thus, in the case of a layerforming method in which the atomic layer deposition method and thephysical vapor deposition method are used together, the layer formingtime can be noticeably shortened compared with the case where the entirelayer 22 having negative electric charges is formed by using the atomiclayer deposition method or the CVD method. As a result, the massproduction efficiency is improved. Furthermore, in the case of theatomic layer deposition method or the MOCVD method, there is almost nodamage given to a substrate compared with a case of forming a layerusing the physical vapor deposition method. Thus, since the damage tothe light receiving sensor portion is reduced, a problem that theinterface state density, which is a cause of generation of a darkcurrent, becomes large can be solved.

Until now, the case in which the layer 22 having negative electriccharges is formed of the hafnium oxide layer has been described. As thelayer 22 having negative electric charges, however, the above-mentionedlayers, for example, the aluminum oxide (Al₂O₃) layer, the zirconiumoxide (ZrO₂) layer, the tantalum oxide (Ta₂O₅) layer, the titanium oxide(TiO₂) layer, the lanthanum oxide (La₂O₃), the praseodymium oxide(Pr₂O₃), the cerium oxide (CeO₂), the neodymium oxide (Nd₂O₃), thepromethium oxide (Pm₂O₃), the samarium oxide (Sm₂O₃), the europium oxide(Eu₂O₃), the gadolinium oxide (Gd₂O₃), the terbium oxide (Tb₂O₃), thedysprosium oxide (Dy₂O₃), the holmium oxide (Ho₂O₃), the erbium oxide(Er₂O₃), the thulium oxide (Tm₂O₃), the ytterbium oxide (Yb₂O₃), thelutetium oxide (Lu₂O₃), the yttrium oxide (Y₂O₃), the hafnium nitridelayer, the aluminum nitride layer, the hafnium oxynitride layer, or thealuminum oxynitride layer may also be used. Also in this case, themanufacturing method according to the embodiment of the presentinvention, in which layer formation is performed by using the atomiclayer deposition method first and then layer formation is performed byusing the physical vapor deposition method, may also be applied in thesame manner. Thus, the same effects as in the case of the hafnium oxidelayer can be acquired.

Next, a solid state imaging device (second solid state imaging device)according to an embodiment (first example) of the present invention willbe described with reference to a cross-sectional view of FIG. 29illustrating the configuration of main parts. In addition, in FIG. 29, alight shielding layer for shielding a part of a light sensing sectionand a peripheral circuit section, a color filter layer for spectralfiltering of light incident on the light sensing section, a condensinglens for condensing light incident on the light sensing section, and thelike are not shown.

As shown in FIG. 29, a solid state imaging device 6 includes a lightsensing section 12, which performs photoelectric conversion of incidentlight, in a semiconductor substrate (or a semiconductor layer) 11. On aside portion of the light sensing section 12, a peripheral circuitsection 14 in which a peripheral circuit (for example, a circuit 14C) isformed with a pixel separating region 13 interposed therebetween isprovided. On a light receiving surface 12 s of the light sensing section(including a hole accumulation layer 23 which will be described later)12, an insulating layer 27 is formed. The insulating layer 27 is formedof a silicon oxide (SiO₂) layer, for example. A negative voltageapplying layer 28 is formed on the insulating layer 27.

In the drawing, the insulating layer 27 is formed thicker on theperipheral circuit section 14 than on the light sensing section 12 suchthat a distance of the negative voltage applying layer 28 from a surfaceof the peripheral circuit section 14 is larger than a distance of thenegative voltage applying layer 28 from a surface of the light sensingsection 12. In addition, when the insulating layer 27 is formed of asilicon oxide layer, for example, the insulating layer 27 has the sameoperation as the interface state lowering layer 21, which has beendescribed earlier, on the light sensing section 12. Accordingly, theinsulating layer 27 on the light sensing section 12 is preferably formedin a film thickness of one or more atomic layers and 100 nm or less, forexample. Thus, when a negative voltage is applied to the negativevoltage applying layer 28, a hole accumulation layer 23 is formed on alight receiving surface side of the light sensing section 12.

In the case when the solid state imaging device 6 is a CMOS imagesensor, for example, a pixel circuit configured to include transistors,such as a transfer transistor, a reset transistor, an amplifyingtransistor, and a selection transistor, is provided as a peripheralcircuit of the peripheral circuit section 14. In addition, a drivingcircuit which performs an operation of reading a signal on a read lineof a pixel array section formed by the plurality of light sensingsections 12, a vertical scanning circuit which transmits the readsignal, a shift register or an address decoder, a horizontal scanningcircuit, and the like are included.

Moreover, in the case when the solid state imaging device 6 is a CCDimage sensor, for example, a read gate which reads a signal chargephotoelectrically converted by the light sensing section to a verticaltransfer gate and a vertical charge transfer section which transmits theread signal charge in the vertical direction are provided as theperipheral circuit of the peripheral circuit section 14. In addition, ahorizontal charge transfer section and the like are included.

The negative voltage applying layer 28 is formed of a transparent andconductive layer which allows incident light to be transmittedtherethrough, for example, a transparent and conductive layer allowsvisible light to be transmitted therethrough. For example, an indium tinoxide layer, an indium zinc oxide layer, an indium oxide layer, a tinoxide layer, or a gallium zinc oxide layer may be used as such a layer.

The solid state imaging device 6 is configured such that a lightshielding layer for shielding a part of the light sensing section 12 andthe peripheral circuit section 14, a color filter layer for spectralfiltering of light incident on at least the light sensing section 12, acondensing lens for condensing light incident on the light sensingsection 12, and the like are provided on the negative voltage applyinglayer 28. As an example of such a configuration, any one of theconfigurations of the solid state imaging devices 1, 2, and 3 may alsobe applied.

In the solid state imaging device (second solid state imaging device) 6,the negative voltage applying layer 28 is formed on the insulating layer27 formed on the light receiving surface 12 s of the light sensingsection 12. Accordingly, by the electric field generated by the negativevoltage applied to the negative voltage applying layer 28, a holeaccumulation layer is sufficiently formed on the interface at a side ofthe light receiving surface 12 s of the light sensing section 12.Accordingly, electric charges (electrons) generated from the interfaceare suppressed. In addition, even if electric charges (electrons) aregenerated from the interface, the electric charges (electrons) do notflow to a charge accumulation portion which is a potential well in thelight sensing section 12 but flow to the hole accumulation layer 23 inwhich many holes exist. As a result, the electric charges (electrons)can be eliminated. As a result, since it can be prevented that theelectric charges generated due to the interface become a dark currentand are detected by the light sensing section 12, a dark current causedby the interface state is suppressed. Furthermore, generation ofelectrons due to the interface state is further suppressed since theinsulating layer 27 serving as an interface state lowering layer isformed on the light receiving surface 12 s of the light sensing section12. As a result, it is suppressed that electrons generated due to theinterface state flow to the light sensing section 12 as a dark current.

Furthermore, as shown in the drawing, since the negative voltageapplying layer 28 is formed such that the distance of the negativevoltage applying layer 28 from the surface of the peripheral circuitsection 14 is larger than the distance of the negative voltage applyinglayer 28 from the surface of the light sensing section 12 by theinsulating layer 27, an influence of the electric field, which isgenerated when a negative voltage is applied to the negative voltageapplying layer 28, on the peripheral circuit section 14 is reduced. As aresult, circuit malfunction in the peripheral circuit section 14 can beeliminated.

Next, a solid state imaging device (second solid state imaging device)according to an embodiment (second example) of the present inventionwill be described with reference to a cross-sectional view of FIG. 30illustrating the configuration of main parts. In addition, in FIG. 30, alight shielding layer for shielding a part of a light sensing sectionand a peripheral circuit section, a color filter layer for spectralfiltering of light incident on the light sensing section, a condensinglens for condensing light incident on the light sensing section, and thelike are not shown.

As shown in FIG. 30, a solid state imaging device 7 is obtained byforming a layer 25 for making a negative voltage applying layer distantfrom a light receiving surface on the peripheral circuit section 14,substantially, between the insulating layer 27 and the negative voltageapplying layer 28 in the solid state imaging device 6. It is preferablethat the layer 25 having positive electric charges in order to eliminatethe influence of negative voltages. The layer 25 having positiveelectric charges is preferably formed between the peripheral circuitsection 14 and the negative voltage applying layer 28. Alternatively,the layer 25 having positive electric charges may be formed on theinsulating layer 27 or below the insulating layer 27. In addition,although the insulating layer 27 is formed as a layer having a uniformthickness in the drawing, the insulating layer 27 may also be formedthicker on the peripheral circuit section 14 than on the light sensingsection 12 like the solid state imaging device 6.

An example of the layer 25 having positive electric charges includes asilicon nitride layer.

Thus, since the layer 25 having positive electric charges is formedbetween the peripheral circuit section 14 and the negative voltageapplying layer 28, the negative electric field generated when a negativevoltage is applied to the negative voltage applying layer 28 is reducedby positive electric charges in the layer 25 having positive electriccharges. Accordingly, the peripheral circuit section 14 is not affectedby the negative electric field. As a result, since it can be preventedthat the peripheral circuit section 14 malfunctions due to the negativeelectric field, the reliability of the peripheral circuit section 14 isimproved. As described above, the configuration in which the layer 25having positive electric charges is formed between the peripheralcircuit section 14 and the negative voltage applying layer 28 may alsobe applied to the solid state imaging device 6, and the same effects asin the solid state imaging device 7 can be obtained.

Next, a method (second manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (first example) of thepresent invention will be described with reference to cross-sectionalviews of a manufacturing process of FIGS. 31 to 33 illustrating mainparts. In FIGS. 31 to 33, a manufacturing process of the solid stateimaging device 4 is shown as an example.

As shown in (1) of FIG. 31, the light sensing section 12 which performsphotoelectric conversion of incident light, the pixel separating region13 for separating the light sensing section 12, the peripheral circuitsection 14 in which a peripheral circuit (for example, the circuit 14C)is formed with the pixel separating region 13 interposed between theperipheral circuit section 14 and the light sensing section 12, and thelike are formed in the semiconductor substrate (or semiconductor layer)11. A known manufacturing method is used as the manufacturing method.Then, an insulating layer 29 which allows incident light to betransmitted therethrough is formed. The insulating layer 29 is formed ofa silicon oxide layer, for example.

Then, as shown in (2) of FIG. 31, a resist mask 53 is formed on theinsulating layer 29 positioned above the peripheral circuit section 14by using resist application and lithography technique.

Then, as shown in (3) of FIG. 32, the insulating layer 29 is processedby etching using the resist mask 53 (refer to (2) of FIG. 31), leavingthe insulating layer 29 on the peripheral circuit section 14. Then, theresist mask 53 is removed.

Then, as shown in (4) of FIG. 32, the interface state lowering layer 21which covers the insulating layer 26 is formed on the light receivingsurface 12 s of the light sensing section 12, actually, on thesemiconductor substrate 11. The interface state lowering layer 21 isformed of a silicon oxide (SiO₂) layer, for example. Thus, theinsulating layer 27 is formed by the insulating layer 29 and theinterface state lowering layer 21.

Then, as shown in (5) of FIG. 33, the negative voltage applying layer 28is formed on the interface state lowering layer 21. The holeaccumulation layer 23 is formed on a light receiving surface side of thelight sensing section 12 by the negative voltage applied to the negativevoltage applying layer 28. Accordingly, at least on the light sensingsection 12, the interface state lowering layer 21 needs to be formed ina film thickness that the hole accumulation layer 23 is formed at a sideof the light receiving surface 12 s of the light sensing section 12 bythe negative voltage applied to the negative voltage applying layer 28.For example, the film thickness is set to be equal to or larger than oneatomic layer and equal to or smaller than 100 nm.

The negative voltage applying layer 28 is formed of a transparent andconductive layer which allows incident light to be transmittedtherethrough, for example, a transparent and conductive layer allowsvisible light to be transmitted therethrough. For example, an indium tinoxide layer, an indium zinc oxide layer, an indium oxide layer, a tinoxide layer, or a gallium zinc oxide layer may be used as such a layer.

A light shielding layer for shielding a part of the light sensingsection 12 and the peripheral circuit section 14, a color filter layerfor spectral filtering of light incident on at least the light sensingsection 12, a condensing lens for condensing light incident on the lightsensing section 12, and the like are formed on the negative voltageapplying layer 28 in the solid state imaging device 6. Any methoddescribed in each example of the method (first manufacturing method) ofmanufacturing a solid state imaging device may be applied as an exampleof the manufacturing method.

In the first example of the method (second manufacturing method) ofmanufacturing the solid state imaging device 6, the negative voltageapplying layer 28 is formed on the insulating layer 27 formed on thelight receiving surface 12 s of the light sensing section 12.Accordingly, by the electric field generated by the negative voltageapplied to the negative voltage applying layer 28, a hole accumulationlayer is sufficiently formed on the interface at a side of the lightreceiving surface 12 s of the light sensing section 12. Accordingly,electric charges (electrons) generated from the interface can besuppressed. In addition, even if electric charges (electrons) aregenerated from the interface, the electric charges (electrons) do notflow to a charge accumulation portion which is a potential well in thelight sensing section 12 but flow to the hole accumulation layer 23 inwhich many holes exist. As a result, the electric charges (electrons)can be eliminated. As a result, since it can be prevented that theelectric charges generated due to the interface become a dark currentand are detected by the light sensing section 12, a dark current causedby the interface state is suppressed. Furthermore, generation ofelectrons due to the interface state is further suppressed since theinterface state lowering layer 21 is formed on the light receivingsurface 12 s of the light sensing section 12. As a result, it issuppressed that electrons generated due to the interface state flow tothe light sensing section 12 as a dark current.

Furthermore, as shown in the drawing, the insulating layer 27 on theperipheral circuit section 14 is formed thicker than the insulatinglayer 27 on the light sensing section 12 such that the distance of thenegative voltage applying layer 28 from the surface of the peripheralcircuit section 14 is larger than the distance of the negative voltageapplying layer 28 from the surface of the light sensing section 12 bythe insulating layer 27. Accordingly, an influence of the electricfield, which is generated when a negative voltage is applied to thenegative voltage applying layer 28, on the peripheral circuit section 14is reduced. That is, since the electric field strength is reduced and itis suppressed holes are accumulated on the surface of the peripheralcircuit section 14, circuit malfunction in the peripheral circuitsection 14 can be eliminated.

Next, a method (second manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (second example) of thepresent invention will be described with reference to cross-sectionalviews of a manufacturing process of FIGS. 34 and 35 illustrating mainparts. In FIGS. 34 and 35, a manufacturing process of the solid stateimaging device 4 is shown as an example.

As shown in (1) of FIG. 34, the light sensing section 12 which performsphotoelectric conversion of incident light, the pixel separating region13 for separating the light sensing section 12, the peripheral circuitsection 14 in which a peripheral circuit (for example, the circuit 14C)is formed with the pixel separating region 13 interposed between theperipheral circuit section 14 and the light sensing section 12, and thelike are formed in the semiconductor substrate (or semiconductor layer)11. A known manufacturing method is used as the manufacturing method.Then, the insulating layer 27 which allows incident light to betransmitted therethrough is formed. The insulating layer 27 is formed ofa silicon oxide layer, for example. Then, the layer 25 having positiveelectric charges is formed on the insulating layer 27. The layer 25having positive electric charges is formed of a silicon nitride layer,for example.

Then, as shown in (2) of FIG. 34, a resist mask 54 is formed on thelayer 25 having positive electric charges positioned above theperipheral circuit section 14 by using resist application andlithography technique.

Then, as shown in (3) of FIG. 35, the layer 25 having positive electriccharges is processed by etching using the resist mask 54 (refer to (2)of FIG. 34), leaving the layer 25 having positive electric charges onthe peripheral circuit section 14. Then, the resist mask 54 is removed.

Then, as shown in (4) of FIG. 35, the negative voltage applying layer 28is formed on the insulating layer 27 and the layer 25 having positiveelectric charges. The hole accumulation layer 23 is formed on a lightreceiving surface side of the light sensing section 12 by the negativevoltage applied to the negative voltage applying layer 28. In this case,the insulating layer 27 may be made to function as an interface statelowering layer. Accordingly, at least on the light sensing section 12,the insulating layer 27 needs to be formed in a film thickness that thehole accumulation layer 23 is formed at a side of the light receivingsurface 12 s of the light sensing section 12 by the negative voltageapplied to the negative voltage applying layer 28. For example, the filmthickness is set to be equal to or larger than one atomic layer andequal to or smaller than 100 nm.

The negative voltage applying layer 28 is formed of a transparent andconductive layer which allows incident light to be transmittedtherethrough, for example, a transparent and conductive layer allowsvisible light to be transmitted therethrough. For example, an indium tinoxide layer, an indium zinc oxide layer, an indium oxide layer, a tinoxide layer, or a gallium zinc oxide layer may be used as such a layer.

Although not shown, a light shielding layer for shielding a part of thelight sensing section 12 and the peripheral circuit section 14, a colorfilter layer for spectral filtering of light incident on at least thelight sensing section 12, a condensing lens for condensing lightincident on the light sensing section 12, and the like are formed on thenegative voltage applying layer 28 in the solid state imaging device 7.Any method described in each example of the method (first manufacturingmethod) of manufacturing a solid state imaging device may be applied asan example of the manufacturing method.

In the second example of the method (second manufacturing method) ofmanufacturing the solid state imaging device 7, the negative voltageapplying layer 28 is formed on the insulating layer 27 formed on thelight receiving surface 12 s of the light sensing section 12.Accordingly, by the electric field generated by the negative voltageapplied to the negative voltage applying layer 28, a hole accumulationlayer is sufficiently formed on the interface at a side of the lightreceiving surface 12 s of the light sensing section 12. Accordingly,electric charges (electrons) generated from the interface can besuppressed. In addition, even if electric charges (electrons) aregenerated from the interface, the electric charges (electrons) do notflow to a charge accumulation portion which is a potential well in thelight sensing section 12 but flow to the hole accumulation layer 23 inwhich many holes exist. As a result, the electric charges (electrons)can be eliminated. As a result, since it can be prevented that theelectric charges generated due to the interface become a dark currentand are detected by the light sensing section 12, a dark current causedby the interface state is suppressed. Furthermore, generation ofelectrons due to the interface state is further suppressed since theinterface state lowering layer 21 is formed on the light receivingsurface 12 s of the light sensing section 12. As a result, it issuppressed that electrons generated due to the interface state flow tothe light sensing section 12 as a dark current.

In addition, since the layer 25 having positive electric charges isformed between the peripheral circuit section 14 and the negativevoltage applying layer 28, the negative electric field generated when anegative voltage is applied to the negative voltage applying layer 28 isreduced by positive electric charges in the layer 25 having positiveelectric charges. Accordingly, the peripheral circuit section 14 is notaffected by the negative electric field. As a result, it is possible toprevent the peripheral circuit section 14 from malfunctioning due to thenegative electric field. As described above, the configuration in whichthe layer 25 having positive electric charges is formed between theperipheral circuit section 14 and the negative voltage applying layer 28may also be applied to the solid state imaging device 6, and the sameeffects as in the solid state imaging device 7 can be obtained.

Next, a solid state imaging device (third solid state imaging device)according to an embodiment (example) of the present invention will bedescribed with reference to a cross-sectional view of FIG. 36illustrating the configuration of main parts. In addition, in FIG. 36, alight sensing section is mainly shown, but a peripheral circuit section,a wiring layer, a light shielding layer for shielding a part of thelight sensing section and the peripheral circuit section, a color filterlayer for spectral filtering of light incident on the light sensingsection, a condensing lens for condensing light incident on the lightsensing section, and the like are not shown.

As shown in FIG. 36, a solid state imaging device 8 has a light sensingsection 12, which performs photoelectric conversion of incident light,on a semiconductor substrate (or semiconductor layer) 11. An insulatinglayer 31 is formed on a side of the light receiving surface 12 s of thelight sensing section 12 and the insulating layer 31 is formed of asilicon oxide (SiO₂) layer, for example. On the insulating layer 31, alayer (hereinafter, referred to as an auxiliary hole accumulation layer)32 having a work function larger than the interface on a side of thelight receiving surface 12 s of the light sensing section 12 whichperforms photoelectric conversion is formed. By a difference between thework functions, the hole accumulation layer 23 is formed. The auxiliaryhole accumulation layer 32 may be an insulating layer 21 or a conductivelayer, such as a metallic layer since the auxiliary hole accumulationlayer 32 does not need to be electrically connected to other elementsand wiring lines.

In addition, on a side of the semiconductor substrate 11 opposite alight incidence side of thereof on which the light sensing section 12 isformed, a wiring layer 53 configured to include wiring lines 51, whichare provided over a plurality of layers, and an insulating layer 52 isformed, for example. Furthermore, the wiring layer 53 is supported by asupport substrate 54.

For example, since the hole accumulation layer 23 is formed of silicon(Si), a value of the work function is about 5.1 eV. Accordingly, theauxiliary hole accumulation layer 32 is preferably a layer having avalue of a work function larger than 5.1.

For example, in the case of using a metallic layer, according to thechronological scientific tables, a value of a work function of aniridium (110) layer is 5.42, a value of a work function of an iridium(111) layer is 5.76, a value of a work function of a nickel layer is5.15, a value of a work function of a palladium layer is 5.55, a valueof a work function of an osmium layer is 5.93, a value of a workfunction of a golden (100) layer is 5.47, a value of a work function ofa golden (110) layer is 5.37, and a value of a work function of aplatinum layer is 5.64. These layers may be used as the auxiliary holeaccumulation layer 32. In addition to the above layers, a metallic layerwith a value of a work function larger than that of the interface at aside of the light receiving surface 12 s of the light sensing section 12may also be used as the auxiliary hole accumulation layer 32. Inaddition, although a work function value of ITO (In₂O₃) used as atransparent electrode is 4.8 eV, the work function of an oxidesemiconductor may be controlled by a layer forming method or injectionof impurities.

It is important that the auxiliary hole accumulation layer 32 be formedin a film thickness, which allows incident light to be transmittedtherethrough, since the auxiliary hole accumulation layer 32 is formedon a light incidence side. Regarding the transmittance of the incidentlight, it is preferable that the auxiliary hole accumulation layer 32have a transmittance as high as possible. For example, it is preferableto secure a transmittance of 95% or more.

In addition, for the auxiliary hole accumulation layer 32, it ispreferable to use a difference between the work function of theauxiliary hole accumulation layer 32 and a work function of a surface ofthe light sensing section 12. Since there is no limitation in lowresistance, it is not necessary to make the film thickness large even ina case when a conductive layer is used, for example. For example,assuming that the intensity of incident light is I₀ and the absorptivityis α (where α=(4πk)/λ, k is Boltzmann's constant, and λ is a wavelengthof incident light), the light intensity at a position of a depth zposition is expressed as I(z)=I₀ exp(−α·z). Accordingly, calculating athickness satisfying I(z)/I₀=0.8, the thickness of the iridium layer is1.9 nm, the thickness of the gold layer is 4.8 nm, and the thickness ofthe platinum layer is 3.4 nm, for example. That is, it can be seen thatthe thickness is preferably 2 nm or less, even though the thicknesschanges with the film type.

In addition, the auxiliary hole accumulation layer 32 may be an organiclayer. For example, polysthylenedioxytyiophene) may be used. Asdescribed above, the auxiliary hole accumulation layer 32 may be aconductive layer, an insulating layer, or a semiconductor layer as longas it has a work function value higher than that of the interface at aside of the light receiving surface 12 s of the light sensing section12.

In the solid state imaging device 8, the layer (auxiliary holeaccumulation layer) 32 with a larger work function value than theinterface 23 at a side of the light receiving surface 12 s of the lightsensing section 12 is provided on the insulating layer 31 formed on thelight sensing section 12. Accordingly, since the hole accumulationefficiency of the hole accumulation layer 23 is improved, the holeaccumulation layer 23 formed on the light-receiving-side interface ofthe light sensing section 12 can accumulate sufficient holes therein. Asa result, a dark current is reduced.

Next, an example of the configuration of the solid state imaging deviceusing the auxiliary hole accumulation layer 32 will be described withreference to FIG. 37. FIG. 37 shows a CMOS image sensor.

As shown in FIG. 37, the light sensing section (for example, aphotodiode) 12, which converts incident light into an electric signal,and a plurality of pixel sections 61 having a transistor group 55(partially shown in the drawing) including a transfer transistor, anamplifying transistor, and a reset transistor are formed in thesemiconductor substrate 11. For example, a silicon substrate is used asthe semiconductor substrate 11. In addition, a signal processing section(not shown) which processes a signal charge read from each light sensingsection 12 is formed.

An element separating region 13 is formed in a part of the periphery ofthe pixel section 61, for example, between the pixel sections 61provided in a column direction or in a row direction.

In addition, the wiring layer 53 is formed on a surface side (below thesemiconductor substrate 11 in the drawing) of the semiconductorsubstrate 11 formed with the light sensing section 12. The wiring layer53 is configured to include the wiring lines 51 and the insulating layer52 which covers the wiring lines 51. The support substrate 54 is formedon the wiring layer 53. The support substrate 54 is formed of a siliconsubstrate, for example.

Furthermore, in the solid state imaging device 1, the hole accumulationlayer 23 is formed on a bottom surface side of the semiconductorsubstrate 11, and the auxiliary hole accumulation layer 32 is formed onthe hole accumulation layer 23 with the insulating layer 31 interposedtherebetween. Furthermore, an organic color filter layer 44 is formedthrough the insulating layer (not shown). The organic color filter layer44 is formed corresponding to the light sensing section 12 and isobtained by aligning a blue organic color filter, a red organic colorfilter, and a green organic color filter in a checker board pattern, forexample. In addition, the condensing lens 45 for making incident lightcondensed onto each light sensing section 12 is formed on each organiccolor filter layer 44.

Next, a method (third manufacturing method) of manufacturing a solidstate imaging device according to an embodiment (first example) of thepresent invention will be described with reference to a flow chart shownin FIG. 38, a cross-sectional view of a manufacturing process of FIG.39, and a cross-sectional view of a manufacturing process of FIG. 40illustrating main parts. In FIGS. 38 to 40, a manufacturing process ofthe solid state imaging device 8 is shown as an example.

As shown in (1) of FIG. 38 and (1) of FIG. 39, an SOI substrate 81obtained by forming a silicon layer 84 on a silicon substrate 82 with aninsulating layer (for example, a silicon oxide layer) 83 interposedtherebetween is first prepared, and a bottom surface mark 85 foralignment is formed in the silicon layer 84.

Then, as shown in (2) of FIG. 38 and (2) of FIG. 39, an elementseparating region (not shown), the hole accumulation layer 23, the lightsensing section 12, the transistor group 55, the wiring layer 53, andthe like are formed in the silicon layer 84 of the SOI substrate 81. Thehole accumulation layer 23 may be formed in a subsequent process after aprocess of making a substrate thin.

Then, as shown in (3) of FIG. 38 and (3) of FIG. 39, the wiring layer 53and the support substrate 54 are bonded together.

Then, as shown in (4) of FIG. 38 and (4) of FIG. 39, a process of makingthe SOI substrate 81 thin is executed. Here, the silicon substrate 82 isremoved by grinding and polishing, for example.

Although not shown, the hole accumulation layer 23 may also be formed byforming a cap layer (not shown) after removing the insulating layer 82of the SOI substrate 81 and performing impurity injection and activationprocessing. As an example, a plasma-TEOS silicon oxide layer is formedin a thickness of 30 nm as the cap layer and the impurity injection isperformed by ion implantation of boron. In this ion implantationcondition, for example, the implantation energy is set to 20 keV and adose of 1×10¹³/cm² is set, for example. In addition, the activation ispreferably performed by annealing in a temperature of 400° C. or less sothat bonding of the wiring layer 53 and the support substrate 54 is notdamaged. Then, the cap layer is removed by rare fluorinated acidprocessing, for example. At this time, the insulating layer 83 of theSOI substrate 81 may be removed.

Thus, as shown in (1) of FIG. 40, the light-receiving-surface-sideinterface 23 of the light sensing section is formed on the light sensingsection 12.

Then, as shown in (2) of FIG. 40, the insulating layer 31 is formed onthe hole accumulation layer 23 (light incidence side). As an example, aplasma TEOS silicon oxide layer is formed in a thickness of 30 nm.

Then, as shown in (3) of FIG. 40, a layer having a work function valuelarger than the interface (having a work function value of about 5.1 eV)at a side of the light receiving surface 12 s of the light sensingsection 12, that is, the auxiliary hole accumulation layer 32 is formedon the insulating layer 31 (light incidence side). As an example, aplatinum (Pt) layer having a work function of 5.6 eV, which is a thinmetal layer, is formed in a thickness of 3 nm by sputtering. For otherthin metal layers, iridium (Ir), rhenium (Re), nickel (Ni), palladium(Pd), cobalt (Co), ruthenium (Ru), rhodium (Rh), osmium (Os), gold (Au),and the like may be used. It is needless to say that alloy may be used.

Furthermore, ITO (In₂O₃) may also be used as a material of the auxiliaryhole accumulation layer 32 since the work function of thelight-receiving-surface-side interface of the light sensing section isabout 5.1 eV in this example. The ITO may have a work function of 4.5 eVto 5.6 eV in the layer forming process. In addition, other oxidesemiconductors, such as RuO₂, SnO₂, IrO₂, OsO₂, ZnO, ReO₂, and MoO₂, ora semiconductor obtained by injecting acceptor impurities, orpolysthylenedioxytyiophene (PEDOT) which is an organic material may alsobe used as a material of the auxiliary hole accumulation layer 32because they have work function values larger than 5.1 eV. In addition,examples of the layer forming technique performed in a temperature of400° C. or less include the ALD method, the CVD method, and the vapordoping method.

Then, as shown in (5) of FIG. 38 and (5) of FIG. 39, a bottom electrode92 is formed through a barrier metal 91.

Then, as shown in (6) of FIG. 38 and (6) of FIG. 39, the color filterlayer 44 is formed on the light sensing section 12 and then thecondensing lens 45 is formed. Thus, the solid state imaging device 8 isformed.

In the method (third manufacturing method) of manufacturing a solidstate imaging device, the layer having a larger work function value thanthe interface 23 at a side of the light receiving surface 12 s of thelight sensing section 12 is provided on the insulating layer 31 formedon the light sensing section 12. Accordingly, since the holeaccumulation efficiency of the hole accumulation layer 23 is improved,the hole accumulation layer 23 formed on the interface at a side of thelight receiving surface 12 s of the light sensing section 12 canaccumulate sufficient holes therein. As a result, a dark current isreduced. In addition, the auxiliary hole accumulation layer 32preferably has a work function value higher than a work function valueof the hole accumulation layer 23 and may be a conductive layer, aninsulating layer 21, or an semiconductor layer since a current does notneed to flow to the auxiliary hole accumulation layer 32. For thisreason, a material having high resistance may also be selected for theauxiliary hole accumulation layer 32. In addition, the auxiliary holeaccumulation layer 32 does not need an external signal input terminal.

Each of the solid state imaging devices 1 to 8 in the above examplesincludes a plurality of pixel sections each having a light sensingsection, which converts incident light into an electric signal, and awiring layer provided on a surface of the semiconductor substrate formedwith the pixel sections, and may be applied as a back illuminatedimaging device having a configuration in which light incident from aside opposite a surface on which the wiring layer is formed is receivedin each of the light sensing sections. It is needless to say that eachof the solid state imaging devices 1 to 8 may also be applied as atop-emission-type solid state imaging device in which a wiring layer isformed on a light receiving surface side and incident light incident onthe light sensing section is not blocked by setting an optical path ofthe incident light incident on the light sensing section as a regionwhere the wiring layer is not formed.

Next, an imaging apparatus according to an embodiment (example) of thepresent invention will be described with reference to a block diagram ofFIG. 41. Examples of the imaging apparatus include a video camera, adigital still camera, and a camera of a mobile phone.

As shown in FIG. 41, an imaging apparatus 500 includes a solid stateimaging device (not shown) provided in an imaging section 501. Animaging optical system 502 which images an image is provided at thecondensing side of the imaging section 501. To the imaging section 501,a signal processing section 503 having a driving circuit for driving theimaging section 501, a signal processing circuit which processes animage photoelectrically converted in the solid state imaging device intoan image, and the like are connected. In addition, the image signalprocessed by the signal processing section may be stored in an imagestorage section (not shown). In the imaging apparatus 500, the solidstate imaging devices 1 to 8 described in the above embodiments may beused as the solid state imaging device.

In the imaging apparatus 500 according to the embodiment of the presentinvention, the solid state imaging device 1 or 2 according to theembodiment of the present invention or the solid state imaging devicehaving a condensing lens and an anti-reflection layer configured asshown in FIG. 4 is used. Accordingly, a solid state imaging devicecapable of improving the color reproducibility or the resolution is usedin the same manner as described above, which is advantageous in that ahigh-quality image can be recorded.

Furthermore, the imaging apparatus 500 according to the embodiment ofthe present invention is not limited to having the above-describedconfiguration but may be applied to an imaging apparatus having any kindof configuration as long as it is an imaging apparatus using a solidstate imaging device.

In addition, each of the solid state imaging devices 1 to 8 may beformed as a one chip type device or a module type device in which animaging section and a signal processing section or an optical system arecollectively packaged and which has an imaging function. In addition,the present invention may be applied to not only a solid-state imagingdevice but also an imaging apparatus. In this case, an effect ofimproving image quality can be obtained in the imaging apparatus. Here,the imaging apparatus refers to a camera or a portable apparatus havingan imaging function, for example. In addition, the ‘imaging’ includesnot only imaging of an image at the time of normal photographing of acamera but also detection of a fingerprint and the like in a broad senseof meaning.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A method of manufacturing a solid state imaging device in which alight sensing section that performs photoelectric conversion of incidentlight is formed in a semiconductor substrate, comprising the steps of:forming an insulating layer on the semiconductor substrate formed withthe light sensing section; and forming a layer having negative electriccharges on the insulating layer so as to form a hole accumulation layerover the light sensing section, wherein forming of the layer havingnegative electric charges includes (a) forming a first layer on theinsulating layer using one of an atomic layer deposition method and ametal organic chemical vapor deposition method, and (b) forming a secondlayer on the first layer using a physical vapor deposition method, thefirst and second layers formed of the same material, and wherein thelayer having negative electric charges is formed of a material selectedfrom the group consisting of hafnium oxide (HfO₂), aluminum oxide(Al₂O₃), zirconium oxide (ZrO₂), tantalum oxide (Ta₂O₅), titanium oxide(TiO₂), lanthanum oxide (La₂O₃), praseodymium oxide (Pr₂O₃), ceriumoxide (CeO₂), neodymium oxide (Nd₂O₃), promethium oxide (Pm₂O₃),samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), gadolinium oxide(Gd₂O₃), terbium oxide (Tb₂O₃), dysprosium oxide (Dy₂O₃), holmium oxide(Ho₂O₃), erbium oxide (Er₂O₃), thulium oxide (Tm₂O₃), ytterbium oxide(Yb₂O₃), lutetium oxide (Lu₂O₃), yttrium oxide (Y₂O₃), hafnium nitride,aluminum nitride, hafnium oxynitride, and aluminum oxynitride.
 2. Themethod of manufacturing a solid state imaging device according to claim1, wherein the first layer is formed using the atomic layer depositionmethod and is formed in a thickness of at least 3 nm of a thicknessrequired for the layer having negative electric charges.
 3. The methodof manufacturing a solid state imaging device according to claim 1,wherein the solid state imaging device is a back illuminated imagingdevice.